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LIBRARY

FACULTY OF FORESTRY
UNIVERSITY OF TORONTO

Cambridge Farm Institute Series

General Editors: T. B.Wood, C.B.E., M.A., F.R.S.

E. J. Russell, D.Sc, F.R.S.

A STUDENT'S BOOK ON
SOILS AND MANURES

CAMBRIDGE UNIVERSITY PRESS

C. F. CLAY, Manager

LONDON : FETTER LANE, E.C.4

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|ij«e^ij

NEW YORK : THE MACMILLAN CO.

BOMBAY 1

CALCUTTA > MACMILLAN AND CO., LTD.

MADRAS J

TORONTO : THE MACMILLAN CO.

OF CANADA, LTD.
TOKYO : MARUZEN-KABUSHIKI-KAISHA

ALL RIGHTS RESERVED

"Tt-

A STUDENT'S BOOK

ON

SOILS AND MANURES

-rA'^ -r-'

BY

E: J. RUSSELL, D.Sc, F.R.S.

DIRECTOR OF THE ROTHAMSTED EXPERIMENTAL STATION
HARPENDEN

SECOND EDITION
Revised and Enlarged

CAMBRIDGE

AT THE UNIVERSITY PRESS

1921

First Edition 1915
Second Edition 19 19
Reprinted 192 1

Printed in Great Britain
hy Tvmbutlis' Spears, Edinlmrgn

SEEN BY
PRESE^: 'ATICM

c. ;•

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PREFACE

WHATEVER kind of farming a man is going in
for, he depends in the last instance either on his
own soil or on somebody else's, and unless he thoroughly
understands the principles of soil management he will
not be very successful in the crop production part of his
work. These principles can of course be acquired by
experience, but the process is likely to be costly, and
the young farmer of to-day is invited to attend Farm
Institutes or Colleges where he can be taught them and
be thus spared some of the bitterness of the older
method. By learning something about the soil and
about fertilisers he will be in a position to attain greater
success in his farming.

But the man who simply studies the subject to make
a little more money will miss nine-tenths of the pleasure
of the work and of the joy of farming. The soil is to be
regarded not simply as a mine out of which a little
wealth may be extracted, but as a part of Nature, just
as wonderful and as worthy of study as any other part.
Whether one is deahng with its history before man
appeared on the scene, the changes that long generations
of farmers have brought about, its remarkable structure
or the infinite wonder of its microscopic inhabitants, it
presents at least as interesting a study as anything else
in this wonderful world of ours. The man who has learnt

aS

vi Preface

to see something in the soil will have a better time at
farming, even if he makes no more money, than the man
who has not.

I hope the student will carry out the experiments
given here as well as those given in my earlier Lessons on
Soil. The analytical methods are put in the Appendix
for the convenience of those who want them ; it is not
intended that all should be carried out by the student
but only such (if any) as may be desirable. I have
assumed no knowledge of chemistry: all the same the
student will need some chemical explanations, but these
must be supplied by the teacher. The vexed question of
how much pure chemistry is needed for an agricultural
course admits of no general answer: the teacher alone
can settle the matter for his own case and to him there-
fore the decision is left.

To my colleague Dr Hutchinson I wish to tender my
best thanks for the care he has bestowed on the photo-
graphs for the book.

E. J. Ri.

rothamsted experimental station,
Harpenden.

Octohtr 1915.

PREFACE TO THE SECOND EDITION

In this edition I have made considerable changes in
the section on Fertilisers and Manures so as to bring in
the new materials and the new points of view that the
War has forced upon us. It is more important than ever
that the young farmer should have clear ideas as to the
why and wherefore of his cultivations and manurings:
if he does not realise exactly what he is doing he can
neither extract the utmost from his soil nor make the
best use of restricted supplies of labour and fertilisers.
No one can dogmatise in agriculture, and no single
method of treatment is always correct. The fundamen-
tal laws of Nature, however, hold good everywhere : it
is the use we make of them that varies. I have dealt
here with these laws ; the more fully the student under-
stands them the better he will be able to use them in
his great work of controlling Nature and making the
earth yield her increase.

E. J. R.

1919.

CONTENTS

PART I. AN ACCOUNT OF THE SOIL

CHAP. PAGE

I What the plant wants feom the soil ... 1

II The composition of the soil 13

III The organic matter of the soil and the changes

it undergoes 36

IV The effect of climate on the soil and on fertility 48

PART II. THE CONTROL OF THE SOIL

V Cultivation 76

VI The control of soil fertility 94

PART III. FERTILISERS

VII The nitrogenous fertilisers 127

VIII Phosphates 140

IX PoTASsic fertilisers 154

X Manures supplying organic matter: Farmyard

MANURE 165

XI Other organic manures 191

XII The purchase and use of artificial manures . 206

XIII Chalk, limestone and limb 219

Appendix 227

Bibliography ........ 236

Index 237

LIST OF ILLUSTRATIONS

FIG.
1.

3.

4.

5.

6.

7.

8.

9.
10.
11.

12.

13.
14.

15.

16.

17.
18.
19.
20.

21.

22.

Tomatoes grown in poor sand, with and without manure

Wheat grown at Rothamsted with varying quantities of
manure ........

Tomatoes with varying water supply
Tomatoes supplied with excess of manure
Tomatoes with varying manure and moisture supply
Curves showing weight of crop produced
Nobel's apparatus for sorting out soil particles
Murray's apparatus for the same purpose
Apparatus for determining carbon dioxide in chalk
Apparatus for collecting carbon dioxide from chalk in soil

Apparatus for demonstrating the presence of carbon
dioxide in soil air ......

Brick chambers hned and floored with cement for experi

ments with subsoil. Photo by Dr H. B. Hutchinson
Dongas in South Africa. Photos by Dr F. H. Hatch

Alkali spot, Fremont, Nebraska. Photo by Dr F. J,
Alway ........

Curve showing amount of nitrate present in soil at
different seasons

The drain gauges, Rothamsted. Photo by Dr H. B,
Hutchinson

Distribution of rainfall in England and Wales .

Distribution of wheat in England and Wales .

Distribution of grass in England and Wales .

Development of prairie land. Western Canada. Photos
by W. F. Oldham and by Staff at Indian Head .

Crop map of Great Britain

Types of furrow-slices ..•,..

PAGE

3

4

5

5

8

9

14

15

26

26

31

33
53

55

60

62
66
67
68

71
73
80

xn

List of BbubviMemM

23L

24.

:caou .

y.»

SL Ha^-i

37. 5.;-.

H.R

L-Tiff^Trttaon

3L

3iL
37.

&5

106

110
IM
li6
157
158
176
^Sl

2L2
2L5

4L

216

227

PART I

AX AOC»?rXI J I^LZ SOIL

CHAPTER I

L_ J~ WVSTS 77 ~ZZ SfflL

nA-^:.. - _: T 7 ^ ->itin»7 -

;.i:iL- - - _ :: .-^ -: - :^:. .^ . JaKwn to hi:

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a _ : IS in

as the jdaee V - . - ect of

tlie seal, its - -T m-

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^<]u.: ire' :
iMi ••«v die 90il fsLjUi^

2 An Account of the Soil [PT. i

is the business ol" plant physiologists to ascertain
plant requirements, and we must therefore start out
with the information they have provided which, how-
ever, we must test for ourselves before we finally
accept it.

Six conditions or factors are known to be necessary
before the plant will make good growth: the soil must
supply a suitable amount of: (1) food, (2) water, and
(3) air; (4) it must be at a proper temperature; (5) there
must be enough of it to afford adequate root room;
(6) it must be free from injurious substances or pests.
What is exactly a suitable amount cannot be stated
beforehand but can only be found out by trial; be-
cause different plants, and even different varieties of
the same plant, have different requirements. Thus an
azalea needs all the six conditions and so does a barley
plant, but the suitable amount is very different in the
two cases. It is unfortunate that no one has yet dis-
covered any way of finding out the suitable amounts
simpler than actual trial because this particular method,
though it looks straightforward, is really very cumber-
some and liable to give misleading results, as we shall
see later on.

All these six conditions are necessary and no one of
them can take the place of any other. If a plant is dying
for lack of water it will not recover by receiving more
food or more air. A proper supply of all the factors
must be maintained, and if any one is insufficient the
plant suffers. This proposition looks simple enough but
the student must fix it carefully in his mind because it
really lies at the foundation of all our work. It is
convenient to use a special name for the condition
the insufficiency of which is preventing the plant from

CH. i] Limiting Factors 3

making better growth, and to speak of it as the "limit-
ing factor." Thus on a dry chalky soil the water supply
is often the limiting factor; if more water is got into the
soil a bigger crop will be obtained. In the cold summer
of 1916 the temperature was on many farms the limiting

Pot No. 47 55 63

Fig. 1. Tomatoes growing on a light sand with varying food supply.

Pot 47, without manure. Pot 55, one dose of manure.
Pot 63, two doses of the same manure.

factor; had the days and nights been hotter the plants
would have made more growth. On poor soils the food
supply is the limiting factor, and addition of more food
in the form of manure will increase the crop. The
problem of successful management of soil fertihty
resolves itself into finding out what is the limiting
factor and then correcting it as cheaply and completely

1—2

An Account of the Soil

[PT. I

Fig. 2. Effect of increasing
dressings of fertilisers on the
yield of wheat, Broadbalk,
Rothamsted.

Plot 3. No manure.

Plot 5. Manure complete ex-
cept for one constituent-
Nitrogen is omitted.

Plot 6. Complete manure con-
taining 43 lbs. Nitrogen per
acre.

Plot 7. Complete manure con-
taining 86 lbs. Nitrogen per
acre.

Plot 8. Complete manure con-
taining 129 lbs. Nitrogen per
acre.

Plot '.i 5

CH. I J Pot Experiments ivith Tomatoes

Pot No. 17
Fig. 3.

Pot 17.
„ 19.
„ 21.
„ 24.

19 21 24

Tomatoes grown in good soil, all equally manured, but

receiving different quantities of water.
No water added.

5 per cent, added, and the moisture then kept constant.
10 per cent, added „ „ „

12J per cent, added „ „ „

i

1

7i ..it

■

1

1

Pot No. 47 55 63 72 79

Fig. 4. Tomatoes supplied with increasing doses of manure.

Pot 47. No manure.

Pots 55 to 79. Increasing dressings of manure. This increases the amount
of growth up to Pot 72 but it depresses growth in Pot 79 where too
much is given. The middle pot, 63, is best for fruit.

6 An Account of the Soil [pt. i

as possible. This is easy on paper but often difficult in
practice.

Where no Hmiting factor is operating it is a general
rule that if any one of the necessary factors is increased
in amount there will be an increase in crop growth. This
is shown in Fig. 1 illustrating three pots of tomatoes
growing in the same soil, sown at the same time and
treated alike in every respect except one. The soil is
a very light sand ; in one pot there has been no addition
of plant food ; in the second the crop has received a dose
of manure, and in the third it has received a larger dose.
A similar result is obtained in the field as shown in Fig. 2 ;
the shortest wheat plant is a representative specimen of
the crop on the unmanured land ; the next plant shows
what happens when an almost but not quite complete
manure is added ; the third shows the marked gain when
one dose of complete manure is given ; next comes the
effect of two doses ; and the last shows the effect of three
doses. In all cases an increase in the amount of plant
food has led to an increase in the crop.

Very similar results are obtained when the water
supply is varied. In Fig. 3 are shown tomato plants
growing in a good soil, sufficiently and equally manured,
and under the same favourable conditions of light,
temperature, air, etc. All the conditions, excepting one,
are the same for all pots: the water supply only varies.
When only little water is given the growth is poor in
spite of the presence of food and the favourable tempera-
ture and light conditions; when more water is added
there is better growth; finally with adequate water
supply growth is really good.

But growth will not go on indefinitely. A fimit is
reached sooner or later beyond which the plant will not

CH. i] Overstepjnng the Limits 7

make any more growth no matter how much food or
water is given. Indeed it is easy to overstep the Umit
and give too much so that the crop actually suffers.
This has happened in the experiment recorded in Fig. 4.
Here, as in Fig. 1, tomatoes are shown growing in soils
provided with different amounts of manure. The first
and second doses of manure resulted in an increased
crop: the third dose caused no further increase: while
the fourth actually caused a decrease, the excess of food
now acting as an injurious substance. This is well seen
also in Pots 27 and 36, Fig. 5 (top row).

The hmit reached in any particular instance, however,
is not necessarily the best growth that can be obtained.
It ma.y be set by the insufficiency of water, of tempera-
ture, etc. Fig. 5 shows in the upper part a set of tomato
plants supplied with successively increasing amounts
of manure and 5 per cent, of water; in the middle a set
supphed with the same amounts of manure and 10 per
cent, of water; and in the lower part a third set also
receiving the same quantities of manure but 12-5 per
cent, of water — this being as much as the soil would
hold. The hmit of growth reached in the first case is
clearly due to a deficiency of water, for it is raised con-
siderablv when more water is added. But a still further
increase in the supply of water does not lead to more
growth, the limit being now set by something else. It
is possible that by increasing the temperature or the
root room we could get more growth out of this last
series, but the process comes to an end before long and
the final limit is set by the sheer inability of the plant
to grow any bigger. If larger crops are wanted it be-
comes necessarj' to try some bigger yielding variety, i.e.
some plant with more power of growth.

An Account of the Soil

[PT. I

Pot No. 3

li

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')

11

20

27

6 per cent.

water.

M

36
36

Pot No. 5

13 21

10 per cent, water.

38

. 1

^^^

i|

*/^W5wm|H»«>

Pot No. 7

39

15 24 32

12| per cent, water.

Fig. 5. Tomatoes grown in soil receiving successively increasing doses of
manure in pots passing from left to right. Pots 3, 5, 7, no manure;
Pots 36, 38, 39, ten doses manure.

Top row : moisture maintained at 5 per cent.
Middle row: „ „ 10 „

Bottom row: ,, ,. 12i

CH. ij Qualitative Differences y

All these results are shown in the curves of Fig. 6.
But there is something more than actual weight. The
student who carries out the experiment will observe
that some of the plants differ very much in appearance
and agricultural or horticultural value even when their
weights are not unlike. Between Pots 3 and 7 (Fig. 5),
for instance, there are great differences. in appearance
and habit of growth. Pot 3 (5 per cent, of water and

u

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S c3

20

lOr

Sand

>;-02

-!<0

73
o

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O

ft

<o •

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H §

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u
^3

O

SO

30

20

10

Soil

10 Water

10 Water

Fig. 6. Curves showing weights of crop produced with varying supplies
of water and 0, 0-01 and 0-02 gram of nitrate of soda per pot.

no nitrate) contains sturdy plants capable of great
development if transplanted into more favourable con-
ditions, while Pot 7 (12| per cent, water and no nitrate)
contains "leggj^" plants that would never be of any
value. Similarly the wetness of the soil affects the root
development : in a dry soil there is more root than in a
wet one: von Seelhorst showed that barley growing in
a soil watered only to half its full water-holding capacity
produced twice as much root as when the water was
maintained at three-quarters the full capacity. These
differences are highly important from the practical point

10 An Account of the Soil [pt. i

of view but they are much more difficult to investigate
than mere changes in weight.

From these and similar experiments we may deduce
three general principles of the highest importance in the
study of soil fertility :

(1) Six separate soil factors are necessary for the
successful growth of the plant: there must be an ade-
quate supply of food, water, air, a suitable temperature,
sufficient root room and an absence of harmful sub-
stances. If any of these conditions is not complied with
the plant fails to grow well: the lacking condition is
called the limiting factor and it must be supplied or in-
creased before further growth takes place.

(2) By increasing the supply of any of the factors
necessary for the plant (food, water, temperature, etc.)
an increase in growth is obtained. But a limit is sooner
or later reached beyond which further growth will not
take place. Additional increases in the food, water
supply, temperature, etc. may do positive harm.

(3) When a crop has been increased by improving
one of the soil conditions {e.g., the food supply, water
supply, etc.) it is always possible that some other factor
which sufficed for the original crop is no longer sufficient
for the new and larger crop. Thus a hmiting factor
comes into play and prevents the farmer from getting
as large a return as he should from his outlay. It is
therefore necessary in all cases where land has been
improved to see that the screwing up of efficiency has
extended to all the six soil conditions, and finally to see
if some new variety of crop with larger power of growth
cannot be obtained that will do even better than the
best of the old varieties.

CH. ij What is Plant Food ^ 11

What is plant food ?

In a general way the grower knows that he feeds his
plants when he gives them stable manure, Uquid manure,
soot, bone meal and other substances. The Ust of plant
foods is very large, indeed probably larger than that of
animal foods. When, however, these foods are examined
by the chemist they are found to owe their value to
the presence of five substances : nitrogen, phosphorus,
potassium, calcium, and magnesium. These there-
fore represent the essential constituents of the foods
supphed. Closer investigation has shown that in ad-
dition sulphur, iron, and probably small quantities of
other substances are needed. These eight or nine
elements are commonly spoken of as the nutritive
elements. They can only be utilised when they are
combined in some way, and as a rule it is in the form
of soluble salts that they are actually taken up by the
plant. Thus the nitrogen is commonly taken in the form
of nitrates or ammonium salts ; phosphorus in the form
of phosphates; potassium, calcium, and magnesium in
the salts of these metals. All these substances occur in
the soil, and they are often spoken of as plant food.

It must be admitted that the term is not entirely
above criticism, because we do not know that all the
substances which enable a plant to grow bigger are really
foods in the ordinary sense of the term. Indeed there is
physiological evidence to show that they are simply the
raw materials out of which the food is made by the
plant for its own use. Further, by far the greater part
of the material of the plant is derived from water, carbon
dioxide, and oxygen, substances which come from the

12 An Account of the Soil [pt. i, ch. i

air and do not figure at all in the above list. But the
term survives because of its convenience.

In later chapters we shall discuss the effect of the
various substances on the plant. For the present it is
sufficient to point out that each individual constituent
element is subject to the same laws as any of the other
soil factors : each must be present to an adequate extent,
and lack of any one cannot be made good by putting in
more of any other. When a soil is deficient in plant food
it need not necessarily receive a complete food: often
only one or two constituents are required. The discovery
of this fact completely revolutionised the practice of
manuring and has enabled farmers to maintain and even
to increase the efficiency of their soils as crop producers
at a minimum of cost. Such partial manuring, however,
has obviously to be done intelhgently or an insufficiency
of something that has been left out may operate as a
limiting factor and prevent the crop making proper
growth. In order to understand the principles involved
it is necessary to make a careful study of the soil and
of the different manures in common use.

CHAPTER II

THE COMPOSITION OF THE SOIL

The reader must often have noticed in walking along
a lane after a heavy rainfall, that the water streaming
down a bank has washed away the soil in a somewhat
uneven manner, leaving behind the grit and small stones
but carrying away the rest. In following the course of
such a streamlet one observes that at certain points a
smooth cake is formed which cracks as soon as it begins
to dry, and is much more sticky and clay-like than the
original soil. Closer observation shows that the original
soil has been separated into various constituents by the
running water, the heavier coarser particles being left
behind while the finer lighter particles are carried on.

This effect of a flowing stream has suggested a inethod
for analysing soil that has proved extremely valuable
and is largely adopted by soil investigators. It consists
in allowing a stream of water to flow over the soil and to
sort out the particles according to their degree of fine-
ness. One form of the apparatus for doing this, designed
by Nobel, is illustrated in Fig. 7. 25 grams of the soil
are put into the smallest of the pear-shaped vessels A,
and water is run in. As the vessels are of different
diameters the water flows through them at different
rates, going most rapidly through the narrowest and
most slowly through the widest, D. When it runs rapidly
it carries away the fine particles leaving only the coarse :
when it goes more slowly it deposits some of the fine
particles. Hence after a time the soil put into the

r i Am Aj^/mmi o/th/t H^Al [wr, i

k^iftmfi wtrf/A ftot into ffoAm, the
fi^i^io^t n^'m the mmikitt remei

A, whSItt tnt: '. « fA mteemmw^ finer par-

till 6mliy the msu> d all pst w»»bed out

into the kuf^ wemv-.^ t..

siUffwifiii mil f/> fall thtonah wa^t/rr, A simple AftpArAttm
dewified Upt tite pwrfyvMr by J, Alar* Murray iii uhown in
P%. ^, A l/>ft^ gk«« tMfj^. aU/ut; .Vj in«, ^/n;? and r/n©
ioA;b flri/1^ k Mfjf'A by rrtf^rm of a iri/i/r pi/yj^r of rn\t\thr
UAte f/> a 200 <;x;, V^rSMttftf^^hr finak wlt.U a nft^;k ori^ ir»r;b
wUSf-. f'/miM(M%% fp-Vh j^ram* of «oil, Tb^ f!a*k i* h^lf-
ftlU-zj i«</t,b «<ar/rr ar</l vij/ofo»i*ly *\iitkt'.u wt hn U* \tr('.ft\c
tif, »,b/T a^/ii tUrfi It, in fi\mfr>X f/nttHtU-^My iWUA with wh.U'.r
ari/i i%tA.it/:U('A U> titf-. U/uu, t»iU:, 7*h^r wUoUr af;paraf.»i.*! i«
now/ fiUM Mp ¥nt}$ wnt/rr an/i tnv*rti/'A tu a v<r»«»:l of
wat/rr, InMtArttiy tUh nftii iritrii'tftM f/t turrthlf. t\irf>\iii)i tUa
WAtfTT, hut Mftffth of it falJA mrtffz (^nif-kly ^.h;u, the- rfmt.

Mffkamctii Anaift^is of Soil

15

\

/

CH. 11 J

The large ooai-i^e particles reaoli tie boTTom of the iiibe
very quickly and form a little layer there, or. if the tube
is left open, they caii be coUecieii in a small dish. Next
come the small but still coarse psxtioles. Alter these the
tine particles begin to come down and at the end the

linest of all settle as a light mud,

More refined methods ai^e in use in
analytical laboratories. The hmips of
soil are lirst broken down by a wooden
j^estle and then by treatment with v^r>-
vlilute acid followed by ammonia. Xext
I he soil is passed through sieves of known
dimensions which sort out the jvarticles
of a certain size. Finally it is stirred
up in a column of water of measurcii
height and ailowied to seitle for a certain
time. The detiiils oi the methvvi an^
giv^n in the Appendix, and the student
is advisevi to carry out an analysis of a
soil with which he is famih.ar. It can be
sliown mathematically that the speev\
with which a jw^rticle sink^ through the
column of water is proportional to the
squart^ of its radius, hence the metho^i
enables us to grade the particles a<WTvi-
ing to their siffc. Numejv»us investiga-
tions have brought out the remarkable fact that the
soil vx>ntains maaiy particles as small as y^hf? i^*-^^
in diameter, while the lai^>e^t particleis in the iii^
earth art^ only some ^ inch in diameter. Siill more nc^
markable }vrha|v< is the fact that no natural divisivxn
usually occtirs K^twtvn the various eonstiment*; the
jv^rticles merge by imperceptible i:: • i^ns m>m the

16 An Account of the Soil [pt. i

very coarsest to the very finest. It is convenient to
make divisions for the purpose of analysis and investi-
gation, but we must not forget that they are entirely
arbitrary and have no existence in nature. In this
country the following grades are adopted:

Diameter of particles
Stones Above 3 mm.

Gravel . . .
Coarse sand
Fine sand
Silt

Fine silt
Clay

Between 3 and 1 mm.
., 1 and 0-2 mm.

0-2 and 004 mm.

004 and 0-01 mm.

001 and 0-002 mm.
Below 0-002 mm.

The clay on the whole possesses a certain set of proper-
ties and the fine silt possesses a different set. Never-
theless one cannot sharply distinguish the clay from the
fine silt because a considerable amount of material
occurs on the border line, possessing some of the pro-
perties of both. Wherever the line is drawn some
material gets included with the clay that behaves rather
like fine silt, and other material is included with the fine
silt that is rather Uke clay. It is equally impossible to
draw a sharp distinction between the silt and the fine
silt on the one hand, and the silt and fine sand on the
other. Wherever limits were selected thev would still
be open to criticism, and the groups adopted in this
country might no doubt be improved upon. Neverthe-
less, so many analyses have now been made here by
this method that no change would be justifiable unless
some great fundamental advantage would be gained
therebv.

The older chemists taught that soil is composed of
two earths: sand and clav. It is now known tiiat this

CH. II J Old Ideas 17

view is incorrect. Soil is not composed of two earths:
it is formed of vast numbers of particles ranging without
any break from the largest to the smallest, and it defies
all attempts at being subdivided into any rigid number
of constituents. As a matter of convenience five or six
groups are distinguished, but we recognise that our
grouping is arbitrary.

The material sorted out in the above experiments can
be used to discover some of the properties of the various
fractions. The coarsest material on examination is
found to be hard and gritty, to dry quickly and to
separate out readily into individual grains. The finest
material, on the other hand, is soft and smooth, it dries
slowly and forms a cake which cracks into little flakes
that curl up in a curious manner. If one of these flakes
is dropped into water it falls to the bottom in one piece,
but if it is rubbed between the fingers under water it
breaks up into particles so minute that they do not
settle but make the water turbid.

The question at once arises: Why are the particles so
different in size ? Why are some so small and others so
large? An obvious answer is that the large particles are
perpetualh^ breaking up into little ones and that the
fine sand represents a sort of half-way .stage between
gravel and clay. This, however, is not entirely correct.
The sand is made of dift'erent material from the clay,
and we can soon see why it has not been reduced to so
fine a state. Put into one test-tube 1 gram of the sand
and into another 1 gram of the clay: add 20 c.c. of
strong hydrochloric acid to each, plunge the test-tubes
into a beaker of boiling water and leave for an hour.
Hydrochloric acid is a potent solvent, and dissolves
material that is not highly resistant. At the end of an

R s. 2

18 Ail Account of the Soil [pt. i

hour the clay is seen to yield a markedly coloured
solution while the sand only gives a slightly yellow
solution: filter these and add ammonia to each until
the liquid turns red litmus blue : the solution from the
sand gives only a shght precipitate while that from the
clay gives a much denser one. Thus we conclude that
sand is much more resistant to the attack of acids than
clay. The same result is obtained when the sand and
the clay are exposed to the weathering agencies: the
sand resists more than the clay and therefore is less
completely broken down. Silt comes in between sand
and clay in point of resistance.

We must now proceed a stage further and try to dis-
cover how the particles got there and what their history
has been.

The origin of the soil particles

The soil particles have originally been derived from
the rocks, and their present state is the outcome partly
of the nature of the rock from which the}^ arose and
partly of the circumstances through which they have
passed. The original rock gradually crumbled by alter-
nate warming and cooling and by the action of water
or ice; the particles formed were carried by wind, by
streams, rivers or glaciers for a greater or less distance
and ultimately found their way to the sea and there
they were deposited. In course of time the pressure of
the great accumulation of material caused some of it to
be converted again into rock and, when the sea-floor
was uplifted to form dry land, this new rock thus ex-
posed went through the same processes of disintegration,
and again the particles were exposed to air, to water
and to ice. Sometimes they remained where they were,

,CH. II] The E feet of Past History 19

or were carried only short distances: sometimes they
were carried away a great distance. In many districts,
as in Central and Eastern Europe, parts of Asia and of
the Middle West of the United States {e.g. in Nebraska),
wind was the transporting agent and the soils thus
formed, known as loess soils, are remarkable for the
narrow range of variation in size of their particles, the
wind only being able to carry particles of certain dimen-
sions. Over much of England north of the Thames, and
the northern parts of the United States, glaciers carried
the particles to their present position, grinding them
sometimes almost to impalpable powder. Elsewhere
flowing water was the transporting agent. From the
moment the original rock solidified right down to the
present day the particles have been subjected to all
those influences of rain, frost, heat and water that are
collectively summed up in the term chmate. The par-
ticles as we find them to-day are largely the result of the
conditions through which they have passed. The past
history of the soil has had an enormous effect on its
present character, indeed in many cases the properties
of the soil were largely settled in geological ages far re-
mote from our own. Thus the red Triassic soils formed
mainly under continental conditions with much wind-
drifted material are quite distinct in character from the
poor clays of the coal measures that preceded them or
the grey soils of the succeeding Lias : all these differ con-
siderably from the Oxford Clays and these in turn from
the Weald Clays.

The rock from which particles originally sprang has
also determined the character of the soil. One of the
commonest mineral substances on the earth is silica, the
chief constituent of quartz, flint, and sand. In these

2—2

20 An Account of the Soil [pt. i

forms it is so hard that it can only be powdered with
difficulty, it is also only very slightly soluble in water.
The sand on the sea-shore affords sufficient illustration
of its properties: in spite of the persistent hammering
of the waves, the washing of the sea and the rain, and
the exposure to all sorts of weather, it undergoes no
perceptible change in any period within the memory of
an individual ; the sand may be carried away but it does
not appreciably dissolve or break down under the in-
fluence of these agencies. The immediate ancestor of
sand is commonly a sandstone rock which is itself com-
posed of grains of sand united by some kind of cement-
ing material. When the rock was exposed to the action
of the weather the cement was washed away and then
the whole structure fell to pieces, grains of sand having
little or no power of holding together by themselves.

This great resistance of sand to the action of water
and weather is its most striking property and gives rise
to consequences of great agricultural importance. It
gives up little or nothing to plants and hence is in no
sense a plant food: indeed plants quickly starve in it.
Its particles show very little tendency to break down
and remain for the most part rather large in size, vary-
ing, as we have seen, from 1 mm. (2^ in.) to 0-04 mm.
(bt5 ill-) ill diameter. Even the edges do not easily wear
away, and the particles remain irregular in outline.
Their large size and irregular shape prevent them from
packing very closely, and large pore-spaces are left in
between. Consequently air gets in very easily, water
rapidly flows through, and the sand speedily dries, at
any rate near the surface.

Another very important group of mineral constituents
also contains silica, but in a state of combination with

CH. ii] The Two States of Clay 21

iron, aluminium, calcium, magnesium, sodium, potas-
sium, etc., forming substances known as silicates. Some
of these, like sand, are very resistant to the action of
water and weather so that they remain as relatively
coarse particles and behave agriculturally like sand.
Others, however, are more easily acted upon with two
important results. Instead of being inert, like sand,
they are reactive, i.e., they will act upon various sub-
stances that may be brought in contact with them, such
as superphosphate, siilphate of potash, etc. The action
of water and weather not only rounds off any edges
they may have possessed, but reduces them so much in
size that they become extraordinarily small and form
the particles which tail off from 0-002 mm. (jjioo ^^O
in diameter to much smaller dimensions. Substances of
this nature are the essential constituents of clay, indeed
the agricultural chemist regards them as the true clay,
any larger inert particles being simply admixtures.

Clay is remarkable in that it can exist in two states ;
one being sticky and the other crumbly or flocculated.
A number of other substances are known that do the
same and they are included in the class known as colloids
— a word that means "like glue." Clay is such a domina-
ting substance that it impresses its properties on the soil
to a considerable extent, hence when the clay is in the
sticky state the whole soil becomes sticky, and con-
versely, when the clay is in the crumbly state the whole
soil becomes crumbly.

Practical men have long since learned that the
crumbly state is good for plants while the sticky state
is not, and they have also discovered how to change one
into the other. Addition of lime, chalk or limestone
causes the change to take place rapidly : organic matter

22 An Account of the Soil [pt. i

(such as farmyard manure, or green crops ploughed in),
frost, and good cultivation also have the same effect.
On the other hand alkaHne manures such as liquid
manure, and manures like nitrate of soda that leave an
alkaline residue in the soil, tend to change the crumbly
back into the sticky state, and if much clay is present
they have a bad effect on the condition of the soil.

These changes are readily, demonstrated by experi-
ment. Stir up some clay in rain or distilled water, pour
off the turbid liquid and divide it into three equal parts.
To one add 5 to lOc.c. of lime water; to another the
same quantity of dilute ammonia solution ; leave the
third alone. Flocculation is seen to take place rapidly
under the influence of lime ; the untreated portion settles
much more slowly; ammonia almost entirety prevents
settling. The effect on drainage can be shown by putting
a layer of clay supported on a perforated disk into each
of three funnels: sprinkle lime on one; pour 10 c.c. of
dilute ammonia solution on to another. Then pour
water on to all three so that it stands at the same height
in each funnel : leave for a time. Percolation begins first
on the limed clay : next on the untreated clay ; but pro-
ceeds only slowly if at all on the clay treated with
ammonia.

More careful experiments have shown that chemically
ptire lime does not flocculate clay but behaves like
ammonia: flocculation only goes on in presence of a
little carbon dioxide which, however, is always present
in the soil.

Silts. Between the inert sand particles and the re-
active clay particles there come a number of others of
intermediate grade differing somcAvhat from either. As
they are smaller than sand they pack together with

CH. ii] . Silts and Silty Soils 23

smaller pore-spaces which retard the movements both
of air and water. Further, they show more tendency to
stick together. Whether or not they have distinct
chemical properties is not clear, nor is it always known
precisely from what minerals they arose. But they con-
stitute a large part of the soil, and have so characteristic
an agricultural effect that they are called by the special
name of silt. It is usual in this country to distinguish
two grades: silt, the particles of which vary in diameter
between 0-04 and 0-01 mm., and fine silt, the particles of
which range between 0-01 and 0-002 mm. in diameter,
but, as already pointed out, the distinction is rather one
of convenience than of reality.

The fine silt differs in one important respect from
elay: it is not flocculated and rendered less sticky by
the addition of hme, or by frost or cultivation. Thus
if a soil contains sufficient fine silt its stickiness and
heaviness cannot usually be remedied by liming, or in-
deed by any method known at present. Such soils occur
on the Boulder Clays, the Lower Wealden Beds in
Sussex, and elsewhere, and they are always a source of
trouble : a good instance is seen at the Leeds University
Farm at Garforth. The simplest plan is to leave them
in grass, but even this device is not entirely satis-
factory.

There is another type of rock which in places has
playecT a great part in the formation of soil. Chalk
covers a large area of the eastern half of England, in-
cluding portions of the counties eastwards of the line
joining Lincolnshire and Wiltshire. Chalk is a substance
of perfectly definite character entirely distinct either
from silica or silicates. It dissolves somewhat in water,
and still more readily in water containing carbon

-4 Ail Account of the Soil [ft. i

dioxide, a gas breathed out bv ourselves, bv animals
and by plants. As aU soil water contains some of this
gas the chalk readily dissolves, so much so that in many
districts,, especially in chalk districts, the spring and
weU waters become very rich in this constituent. It
deposits on boiling and forms a fur in boilers, kettles,
etc. ; sometimes it even deposits on standing, forming a
sediment in the vessel or a crust on any object Ivinor
in the water. Chalk is decomposed by strong heat givincr
off carbon dioxide gas and leaving hme behind: this is
the change that goes on in a hme kiln. Careful studies
of the decomposition have proved that 100 parts by
weight of pure chalk, after the removal of all impurities,
invariably give rise to 56 parts by weight of hme and
4A parts by weight of carbon dioxide. This relationship
.is very important for it shows how chalk is built up: it
may be expressed thus :

Chalk or calcium carbonate = lime or calcium oxide -i- carbon dioxide

IW 56 44 parts by weight.

The effect of carbon dioxide in promoting the solution
of chalk is shown by the following experiment: Take
some fresh rain-water and divide into two lots of 100 c.c.
each : to each add 1 gram of finely powdered quarrv or
precipitated chalk. Shake one lot occasionally: blow
your breath (which contains carbon dioxide) through
the other at intervals during five minutes. Then leave
for a Httle time to settle. Pour each hquid through a
separate filter, measure 50 c.c. of each into beakers and
evaporate on the water-bath. Although the filtered
Hquid was perfectly clear it is seen to leave a distinct
residue after the experiment, showing that some of the
chalk has been dissolved: a larger quantity of residue is

CH. ii] Chalk and its Composition 25

found in the water through which carbon dioxide was
blown.

What has happened chemically is that calcium car-
bonate in presence of carbon dioxide and water becomes
converted into calcium bicarbonate which is soluble in
water but readily decomposes on boiling into calcium
carbonate once more.

A much quicker way of dissolving calcium carbonate,
and one largely used in laboratories, is to treat it with a
strong acid, when decomposition takes place and carbon
dioxide is evolved. 100 parts of calcium carbonate give
rise to 44 parts of carbon dioxide just as it did on heat-
ing, but the remainder, instead of appearing as calcium
oxide, appears as a salt. Thus if sulphuric acid is used
the reaction is :

Calcium carbonate -r sulphuric acid = calcium sulphate -r carbon dioxide
100 44 parts bj weight.

This reaction is so important that it must be studied in
an actual experiment. Weigh out 0-5 gram of calcium
carbonate^ in a 50 c.c. conical flask, put in a small tube
of strono: hvdrochloric acid, cover the calcium carbonate
with water, and then stop the flask with a cork bored
with two holes, one to admit a tube passing to the
bottom of the flask, the other to hold a tube that just
dips into the flask and then connects with a wide tube
holding calcimn chloride, a powert'ul agent for absorbing
water vapour (Fig. 9). CarefuUy wipe the whole appara-
tus with a soft duster, leave it standing for a time in the
balance case and then weigh, Xext tilt the acid gently

^ Whiting is a stifficiently pure form. If it is not convenient to weigh
the gas as described above, the volume can be measured and the weight
calculated in the usual way. 1 c.c. of CO* at 0' C. and 760 nun. pressure
weighs 0-002 gram.

26

An Account of the Soil

[PT. I

on to the calcium carbonate and see how the carbon
dioxide is given off. After effervescence ceases blow air
gently through the tube A to displace the carbon dioxide
and then weigh again. The loss of weight represents the
carbon dioxide.

Next treat some soil with sulphuric acid. If there is
vigorous effervescence you can proceed to study the gas
evolved. Put some soil into a 250 c.c. flask fitted with

Fig. 9. Apparatus for determining
carbon dioxide in chalk.

Fig. 10. Collection of carbon di-
oxide from a soil rich in chalk.

a thistle funnel and delivery tube : pour sulphuric acid
— 1 part of acid to 1 of water — on to the soil and collect
the gas over the water (Fig. 10). Put a lighted taper to
the jar: the gas will neither burn nor will it allow the
taper to burn. Pour in some clear lime water: a dense
milkiness is produced. Collect another jar of the gas and
stand it over caustic soda. The gas is rapidly absorbed
and the soda rises in the jar. A third jar can be used to
demonstrate the heaviness of the gas as compared with
air: pour the gas into an empty jar containing some clear
lime water: a milkiness is produced. Now all these

CH. iij Carbonates in the ISoil 27

properties are identical with those of the gas obtained
from chalk treated in the same manner, and we can
therefore conclude that the gas evolved is carbon dioxide
and further that a carbonate is present in the soil. We
cannot say what carbonate, because as a matter of fact
all carbonates would decompose under the same circum-
stances to give carbon dioxide. There is evidence to
show that calcium carbonate is the chief one in the soil
and it has become customary to speak as if this were
the only carbonate, although it is known that others
also occur. Thus in forming estimates of the amount of
carbonate in the soil it is usual to determine the amount
of carbon dioxide evolved and then express this in terms
of calcium carbonate.

The experiment made with the calcium carbonate
(Fig. 9) should now be repeated with soil. The precise
amount to be used depends on the amount of effer-
vescence with the acid : if this is vigorous 10 to 20 grams
may be sufificient: if not 25 grams may be needed, while
in many cases the method may break down altogether
and another has to be adopted. If there is only shght
effervescence it is unlikely that the soil contains more
than 0-5 per cent, of carbonates, while many soils con-
tain less.

Colhn's calcimeter^ is a more convenient form of appa-
ratus for measuring the amount of carbon dioxide given
off from soil, and therefore the amount of carbonate
present.

The calcium carbonate in the soil arises from several
sources. The huge masses of chalk represent the remains
of minute sea animals, as may be seen by examining

^ See Journ. Soc. CJmri. Ind. 1906, 25, 518. The apparatus is made
by Messrs Brady and Martin, Newcastle-on-Tyne.

28 An Account of the Soil [pt. i

some of it under a microscope. The chalk has often been
distributed to other soils, sometimes by flowing water
and sometimes by glaciers as in the chalky boulder clay
of the eastern counties. A second mode of origin of
calcium carbonate is from the weathering of rocks, and
a third from the decomposition of plant and animal re-
mains. A good deal of chalk, however, has been added
to the soil by farmers in the past : some of the fields in
Hertfordshire still contain as much as 1 or 2 per cent,
put on as top dressings 50 years or more ago.

The constituents dealt with in the preceding para-
graphs— the various sands, silts, clay and the chalk —
compose almost the whole of the mineral part of the
soil. But although the balance is only small in amount
it is of great importance to the plant, for it contains an
essential article of plant food — calcium phosphate. This
substance arose in the first instance from the rocks, but
often the material in our soils has already done duty in
past ages, and has helped to build up the skeleton of
some organism, on the death of which it has again re-
turned to the soil to do duty once more. It is readily
detected by heating 20 grams of soil with concentrated
hydrochloric acid on a water-bath for an hour, filtering,
and adding to the filtrate a solution of ammonium molyb-
date^. A yellow precipitate comes down containing the
phosphoric acid extracted by the hydrochloric acid.

The red or yellow colour of the solution is due in part
to the iron present. On neutralising with ammonia a
dense red precipitate containing iron and aluminium
oxides comes down and can be filtered off : the presence
of iron can then be confirmed by the beautiful blue pre-
cipitate obtained when the red material is dissolved in

^ 8ee Appendix, p. 233.

CH. II J Phosphates and Potassium Compounds inSoil 29

a little hydrochloric acid and treated with potassium
ferrocyanide solution, or by the very deep red colour
obtained when some of the hydrochloric acid solution
is almost neutralised with ammonia and then treated
with potassium sulphocyanide solution.

Another constituent of the hydrochloric acid extract
of the soil is potassium which occurred in the complex
sihcates of the soil. Unfortunately there is no very
simple way of demonstrating its presence, but a method
for laboratory use is given on p. 229. Both phosphorus
and potassium salts are essential plant foods and among
the most important constituents of the soil from the
farmer's point of view. Yet they do not form any very
great proportion of the whole and even in a fertile soil
there is often not more than three or four lbs. of either
in a ton of soil whilst the amount that plants can get
hold of may only be a few ounces. The plant, however,
does not want a great deal; one ton of mangolds only
contains some 10 lbs. of potassium and 1| lbs. of phos-
phorus^ so that the quantities present are not as in-
adequate as they appear.

We have now come to an end of the importa.nt mineral
constituents of the soil. When such a soil is supplied
with water, is properly aerated, and receives a sufficient
amount of heat from the sun, it speedily becomes the
abode of many plants and animals. As these die their
remains mingle with the soil, and so a fresh constituent
appears, known as organic matter, which has the dis-
tinguishing characteristic that it got there through the
agency of hving organisms and has the chemical dis-
tinction of being easily and completely burnt away.
The presence of this organic matter is easily shown by

^ In accordance with British custom these amounts are stated as the
oxides KjO and P2O5.

30

An Account of the Soil

[PT. I

heating some soil on a tin lid or in a crucible; the soil
blackens or chars, then little sparkles of fire can be seen,
and finally all the combustible part smoulders away
leaving only the mineral constituents. The organic
matter is so important that it must be dealt with in a
separate chapter by itseK.

It has become customary to talk of the "nitrogen,"
"pLosphoric acid," "potash," "lime," etc. in the soil,
but the student must at the outset reaHse that these do
not exist as such in the soil. The nitrogen meant is not
nitrogen as it occurs in the air, and which is better
spoken of as gaseous nitrogen: it is nitrogen combined
with other substances. "Phosphoric acid" does not
occur in the soil, but only its compounds, the phos-
phates; "potash" and "hme" do not occur, but only
potassium and calcium salts. These distinctions must
be clearly grasped: failure to understand them will re-
sult in considerable confusion later on.

The mineral and organic constituents, however, do
not form the whole of the soil mass, but only one-half
to two-thirds of it; the remainder is filled with air and
water which are of vital importance to the roots of the
plants and to the soil organisms. The air resembles
ordinary atmospheric air in composition, but it contains
more carbon dioxide and more water vapour :

Oxygen

per cent.

by volume

Xitrogen

per cent.

by voliuiic

79-02

79-2

SO-2

Carbon

dioxide

per cent.

by volume

Atmospheric air
Soil air, arable
Soil air, pasture

20-95

20-5

18-2

0-03

0-3

1-6

CH. II j

The Soil Air

31

When the soil becomes waterlogged, however, the
percentage of oxygen may fall very considerably so that
insufficient is left for the organisms to carry on their

A

Fig. 11. Apparatus for demonstrating the presence of CO2 in soil air.

A. Aspirator.

B. J" gas pipe driven into soil.

C. Tube of baryta water open to air.

D. „ „ connected to soil.

usual functions. Undesirable changes may then set in.
The presence of more carbon dioxide in the soil air than
in the atmosphere is readily demonstrated by driving a
I inch gas pipe to a depth of 6 inches in the soil and con-
necting it with a test-tube containing 20 c.c. of baryta

32

An Account of the Soil

PT. 1

water and attached to an aspirator. A similar tube also
containing 20 c.c. of bar3^ta water but open to the air is
attached to the same aspirator. Set the aspirator work-
ing and arrange the connections so that bubbles pass at
the same rate through the two lots of baryta water. The
one connected with the soil speedily becomes turbid, in-
dicating the presence of carbon dioxide, the other, open
to the air, however, only shows turbidity later on
(Fig. 11).

The water is held by physical forces in the pores and
the amount present depends on the rainfall, the evapora-
tion and the drainage. In the Rothamsted measure-
ments the sandy soils were generally found to contain
about 9 per cent., the loams about 12 per cent., and the
clays about 27 per cent, by weight; a better idea, how-
ever, is furnished by taking the proportions by volume,
which varj' from 20 to 40 per cent. The following are
the figures for some of the Rothamsted soils :

Vol. occupied in y^j^^^ ^j ^^^^^
natural state by

Volume of air

Solid
matter

Air and
water
(pore-
space)

In

normal

moist

state

After
period

of
drought

In

normal

moist

state

After
period

of
drought

Poor heavy loam
Heavily dunged arable
pasture

66
62
53

34
38
47

23

30
40

17
20
22

11

8
7

17

18
25

The water is not pure but contains various salts in
solution, the most important of which are nitrates and
bicarbonates (p. 25).

The subsoil. The lower portion of the soil differs so
much from the surface layer that it receives a separate

CH. II J

The Subsoil

33

c3

^-^

>>

a>

-f->

^

CO

Eh

a

cS

^

o

■S

s

3

<4->

Ut

tn

o

~4-^

to

a

c

'S

'?

-o

.^

e3 o

S ID

O -'^

^ a

•- o

0

^

0

s

0

M

a<

M

a

■n

cj

c3

ti

<D

E

R. S.

34 An Account of the Soil [pt.i

name and is called the subsoil. The dilference lies in
the fact that neither plant nor animal life has been able
to exert any great effect, so that the subsoil contains
very little more than the original mineral material. It
contains less organic matter than the surface soil, and
in consequence has not the satisfactory physical proper-
ties conferred thereby and it possesses less nutrient
plant material. Usuallj^ also it contains more clay and
this is present in the sticky rather than in the crumbly
form. Both causes combine to render the subsoil less
tractable than the surface soil, and on heavy soils it may
become so bad that it must on no account be brought
to the surface. Indeed many acres of land have been
ruined by deep steam ploughing which has buried the
surface soil and only left the plants with a sticky un-
kindly subsoil. An advantage of the one-way or turn-
wrest plough is that it does not, hke the ordinar}^ plough,
leave furrows of barren subsoil throughout the field be-
tween each of the lands.

The following experiment has been started at Roth-
amsted and might advantageously be tried elsewhere.
Select some suitable site in the experimental field or
garden and construct therein two brick chambers each
20 inches deep and 7 ft. square, with cement floor and
Mning, making a way out for drainage -water (Fig. 12).
Fill both with subsoil obtained during excavations for
a building or dug specially. Leave one entirely alone
and observe the changes it undergoes: sow the other
with crops and observe their manner of growth.

Plough Soles and Pans. At a depth of 4 or 5 inches
below the surface of the soil there is sometimes a hard
layer through which penetration is difficult. This is
called a plough-sole ; it is the result of persistent plough-

CH. ii] Plough Soles and Pans 35

ing to the same depth ; the weight of the plough pressing
on the bottom of the furrow causes a certain amount of
consoHdation which in course of time becomes very-
mar ked.

In soils where water is near the surface a layer of rock
known as a pan sometimes occurs. It is formed by the
precipitation of soluble material through a process similar
to the formation of certain jeUies.

Plough-soles and pans should be broken by occasional
deep cultivation so as to allow free movement of the
water and deep development of plant roots.

3—2

CHAPTER III

THE ORGANIC MATTER OP THE SOIL AND
THE CHANGES IT UNDERGOES

The organic matter of the soil represents, as we have
seen, the remains of previous generations of plants and
animals and can roughly be sorted out into two divisions
according to age : some of it is as old as the soil, having
been deposited along with the mineral particles when the
soil was first made ; some of it is newer, representing the
residues of recently living plants. It is not known
whether the original organic matter has any particular
effect on the soil, but one generally supposes that it has
not. Its properties have been studied by examination
of the subsoil at a depth below the range of the surface
vegetation.

The more recent material is of supreme importance to
the soil. It is subdivided into (a) the newest of all, the
undecomposed roots or stubble which still retain some
of the structure of the plant; and (6) the partly decom-
posed material, dark brown or black in colour, which
has fallen entirely to powder and become completely
intermingled with the soil ; this part is commonly called
"humus." The undecomposed part serves two pur-
poses: it is the source from which the humus is derived,
and it keeps the soil open and porous, maintaining
passages through which water can drain away and air
can enter, and preventing the mineral particles from
settling down too compactly. In glasshouse practice it
is always desirable to keep up the supply and this is

CH. Ill] Undeconii^osed Residues 37

done by mixing good fibrous turf in the borders {e.g.,
cucumber borders) so that the soil shall always remain
open and aerated in spite of the constant heavy water-
ing. After a time the fibrous roots disappear and then
the soil is much more likely to become sodden, covered
with green growths, and "sour," than it was while the
fibre lasted. In outdoor horticultural work it is equally
an advantage to have sufficient undecomposed or fibrous
material to keep the soil open, and afford what the
gardener' calls a proper root run. On heavy farm soils,
also, undecomposed material, such as stubble, straw,
long manure, is very helpful for the same reason. On
the other hand this material is a disadvantage on Hght
soils because these are already open enough especially
in dry seasons. Any fibrous or undecomposed plant
material or manure containing long straw or peat moss
is therefore added in autumn so that it may have a
good chance of being broken up before the summer
droughts come on. On many good light-land farms,
indeed, the use of these materials is reduced to a
minimum by a method that will be discussed later
(p. 113).

This fibrous material contains many of the chemical
substances that occur in the plant: among them are
protein, cellulose, and waxes. The decompositions that
go on in the soil are not known in full detail, but it has
been found that the protein breaks down to form
ammonia and other substances, some of which, along
with the cellulose, give rise to the black mixture humus ;
carbon dioxide is also given off during the process. There
must be many products formed during these decom-
positions, but very httle is known of them with cer-
tainty. The waxes only disappear slowly; they tend to

38 An Account of the Soil [pt. i

accumulate on'soils like old garden soils to which much
plant matter is added, and they are probably partly
responsible for the curious difficulty in wetting these
soils when once dry ; drops of water tend to stand on the
surface and not to soak in.

The mixture known as humus plays a specially im-
portant part in soil productiveness. In days gone by
humus was regarded as a distinct chemical group and
was subdivided into humic acid, ulmic acid, crenic acid,
aprocrenic acid, etc., but it is now known that these
substances are only imaginary; we shall therefore not
concern ourselves with them. Humus is a mixture which
is not yet satisfactorily resolved into its component
parts.

Some of it can be extracted from the soil by means
of dilute alkahs, by the following method. Shake 100
grams of soil with 500 c.c, of 5 per cent, hydrochloric
acid, allow to settle, pom' off through a filter, and wash
with water. Then transfer the soil to a bottle, add
500 c.c. of 5 per cent, caustic soda solution, shake, and
leave for some hours lying on its side so that as large
a surface as possible is exposed to the alkah: shake
periodically. Before long the alkah becomes dark
coloured. Again allow to settle and syphon off, or, if
you can, filter on the Buchner funnel by aid of the
pump : this is rather a slow process. To the clear dark
coloured filtrate add some strong hydrochloric acid drop
by drop till the hquid is just acid. A dark brown pre-
cipitate is thrown down containing much of the organic
matter. Some, however, still remains in solution : a part
of this can be brought down by exactly neutrahsing
with caustic soda, but the rest is only recovered by
evaporation. It is sufficient, however, to examine the

CH.[iii] Soluble Humus 39

precipitate. On drying, this shrinks very much to little
lumps almost black in colour which readily burn and
leave behind a Httle red ash. Its composition varies con-
siderably, but after it is thoroughly dried in a steam
oven it usually contains about 50-57 per cent, of carbon,
35 per cent, of oxygen, and 3-8 per cent, of nitrogen.

The soil which has thus been treated still contains
more of the soluble material, and several successive ex-
tractions have to be made with alkah before anything
like exhaustion appears ; even then soluble material still
continues to come out although the solution is no longer
dark coloured. But even after numerous extractions a
considerable amount of the organic matter — often about
one-haK of the original quantity — remains in the soil.
Some of this is capable of being transformed into soluble
substances by heat : thus if a fresh portion of the soil is
heated by steam at 100° C. for an hour and then sub-
mitted to the extraction processes already described, a
considerably larger amount of material dissolves out in
the alkah than before.

The chemical nature of these various substances is
under investigation at the Bureau of Soils, Washington,
and at Rothamsted. From the Rothamsted experi-
ments it does not appear that the "soluble humus" is
of particular value in soil fertility though humus as
a whole is highly important. The physical effects of
"humus" will be taken in detail in Chapter VI; they
faU under three headings :

1. The organic matter imparts a black colour to the
soil unless there happens to be a good deal of chalk
present, when the white colour persists. It is a weU-
known physical law that a black substance absorbs
more heat than a white one placed under similar con-

40 An Account of the Soil [pt. I

ditions, hence the dark colour facilitates the warming
of the soil in spring.

2. The organic matter greatly increases the capacity
of the soil for holding water. A soil rich in organic
matter is throughout the summer and autumn dis-
tinctly moister than a soil poor in organic matter

(p. 181).

3. Organic matter facilitates the production of a fine
tilth and a good seed bed, and it renders cultivation
more easy.

Soils well supphed with organic matter are therefore
very valuable to the agriculturist both by reason of the
large amount of nitrogenous substances they contain
and also because of the ease with which they can be
worked. Examples occur in the fen districts in this
country, in the prairies of Western Canada, the black
earth or Tchernozem of Russia and elsewhere. Wherever
they occur these black soils are promptly taken up for
cultivation.

There is, however, another type of organic matter
which is less widely distributed and much less useful.
Peat is organic matter but it is too acid and not suffi-
cientty decomposed to be of much value, hence peaty
soils are not in high agricultural repute. Intermediate
between peat and fen comes another type found in the
carr soils, which can be made distinctly useful by dress-
ings of lime. Owing to the great importance of the
organic matter chemists have made many attempts to
determine just how much is present in the soil. Advan-
tage is taken of the fact that organic matter bums away
while mineral matter does not: hence some of the soil
is burnt, and the loss of weight is measured (p. 227).
This method is simple, but unfortunately it is not quite

CH. Ill] Determination of Organic Matter 41

sound, for some of the mineral matter undergoes changes
on heating accompanied by alterations in weight. Nor
does the method discriminate between the undecom-
posed and the decomposed material which as we have
seen behave very differently in the soil. In some labora-
tories {e.g., at Rothamsted) the larger fragments of un-
decomposed material are removed by sifting and blow-
ing, and estimated separately. But more usually the
whole of the material is estimated together.

Another method of discovering how much organic
matter is present in the soil is to determine the per-
centage of nitrogen (p. 228). This is important because
it gives an indication of the nitrogen reserves in the soil,
but again it tells us nothing about the state in which
these exist and whether they are useful or not. Table I
gives typical examples and shows that there is no very
clear connection between the productiveness of the soil
and the percentage of nitrogen or the loss of organic matter.

Table I. Percentage of nitrogen and organic matter
m typical soils and subsoils

Fertile arable soils

Surface Soils

Loss on ignition 4-65

6^58

3^70

4^65

Nitrogen

•120

•220

•133

•141

Subsoil

Loss on ignition 3-00

4-94

2^81

3^29

Nitrogen -078

•139

•081

•097

Poor arable soils Barren wastes

Surface Soils

Loss on ignition

4-13

6-23 3-60

514

5^94 1 7-00 i 5^81 j

Nitrogen

•128

•143 ^182

•152

•130

•195 1 ^167

Subsoil

1

1

Loss on ignition

3-74

5-50 2^58

4^14

2^70

Nitrogen

•112

•104 -061

•096

•058

42 An Account of the Soil [pt. i

Nevertheless the results are of much value to the agri-
cultural chemist in investigating soil fertihty problems.

We must now turn to the changes undergone by the
organic matter. During the process of cultivation the
organic matter becomes oxidised and some of it dis-
appears as gas ; it thus suffers much more rapid changes
than the mineral particles. Illustrations can be seen in
parts of North America where the original prairie soil
was fairly rich in organic matter but after some years
of wheat cultivation it has lost much of its stock. In
Minnesota Snyder found that an amount containing 50
per cent, of the nitrogen was lost in twenty years' culti-
vation: in Saskatchewan Shutt observed a loss of an
amount containing 30 per cent, of the nitrogen after a
similar period. With the organic matter is lost also the
advantages it conferred : the soil becomes impoverished,
and, if much clay is present, it becomes difficult and
expensive to cultivate. Hence such soils tend to be
thrown out of cultivation and to become derehct.
Similar losses occur in market gardens and wherever
large dressings of farmyard manure are appUed: they
necessitate the use of more manure than is really needed
by the plant and they add to the expense of production.

A closer analysis of the loss shows that the carbon of
the organic matter goes off as carbon dioxide and that
some at any rate of the nitrogen is changed to ammonia,
and there is evidence that some is lost as gaseous nitro-
gen. The question is under investigation at Rothamsted;
it is of enormous agricultural importance because of the
seriousness of the loss on rich soils and the necessity for
reducing all wastage nowadays: it is discussed more
fully in Chapter VI.

The ammonia remaining in the soil is at once seized

CH. iir]

Nitrijication

43

upon by certain soil bacteria, the Nitrosomonas, and
converted into a nitrite, and this taken by another group
of organisms, the Nitrobacter, and converted into
nitrate; the process is called nitrification. Thus the
ammonia actually appears as nitrate which is readily
found in the soil by the simple test given in the Appendix
(p. 228). The amount of nitrate is commonly stated as
so many parts of nitrogen per million parts of soil ; they
can be expressed as parts of nitrate of soda by multi-
plying by 6, or they can be converted into lbs. per
acre in the top 9 inches by multiplying by 2|; the
results are not quite accurate but suffice for purposes
of comparison.

The following amounts of nitrate were commonly
found in the author's investigations of various soils:

Expressed as nitrogen

Expressed as nitrate
of soda

Parts per million
0-9" 9-18"

Lbs. per acre
0-18"

Lbs. per acre
0-18"

Sand

Loam

Clay

5
10
10

4

8
6

25
46
38

150

276
228

Nitrates do not accumulate to any great extent in the
soil in our climate, and it is very unusual to find more
than 24 parts per milhon or 120 lbs. per acre (expressed
as nitrogen) in the top 18 inches. As soon as these high
values are reached further production ceases. It some-
times happens in dry regions that higher amounts are
present, but it is usually supposed that they got there
by evaporation of water which has soaked in from some-
where else, concentrating the nitrates from a wide area
over a particular spot.

44 An Account of the Soil [pt. i

Under our climatic conditions the nitrates do not get
the opportunity of persisting long but are either washed
out by rain or taken up by plants. Once the stock is re-
duced a further quantity begins to be formed and so far
no hmit has been reached to the amount of nitrate a
soil can be made to yield. One of the Rothamsted plots
which has been cropped with wheat every year since
1843 and has had no manure since 1839 still goes on
yielding nitrate and in September 1913 contained nearly
35 lbs. of nitrogen as nitrate, equivalent to 210 lbs. of
nitrate of soda in the top 18 inches of soil per acre.
Another piece of land is kept bare of all vegetation and
is undermined in such a way that the whole of the
drainage-water can be collected for analysis. Ever since
1870 when the experiment began the land has yielded a
large supply of nitrate, the amount being equivalent to
300 lbs. of nitrate of soda per acre every year for the first
20 or 30 years, and to some 170 lbs. in more recent years.

A further change goes on in certain circumstances.
When all air is excluded from the soil by flooding it for a
long time with water, the nitrates are hable to decompose
yielding nitrites and subsequently gaseous nitrogen. This
change, kno"WTi as denitrification, only goes on slowly in
cold weather and probably is of rare occurrence under
British agricultural conditions where land would only
be waterlogged in winter, if at all. But it seems to go on
in the wet rice fields of the East and in these circum-
stances nitrates are not used as manure.

All these changes result in loss of nitrogen : fortunately
there are others that bring about gains, chief among
them being the fixation of gaseous nitrogen by the
organisms in the root nodules of leguminous plants.
Some also is fixed by certain free Mving bacteria called

CH. iiij Nitrogen Fixation 45

Azotobacter. These require considerable quantities of
decaying plant residues as a source of energy: for the
process is not one that will continue by itself once it is
started like the burning of a bonfire, but rather it re-
sembles hauhng a load up a hill and requires the con-
tinuous application of energy. The fixation through the
root nodules proceeds vigorously during the growth of
clover, trifolium, lucerne, sainfoin, vetches, etc., and
these crops therefore enrich the soil considerably. Both
processes take place in land laid down to grass. The
gain does not go on indefinitely: after a time it is
counterbalanced by losses; but the net result is that
grass land contains considerably more nitrogen than
arable land. The nitrogen comes from the atrnosphere,
and thus represents an absolute gain to the stock in the
soil. The following simple rule should be remembered
by the student : land in sod gains nitrogen, land in fallow
gains nitrate. The gain in nitrogen is absolute, but the
gain in nitrate is not, it only represents a change of one
form of soil nitrogen into another. When the grass land
is ploughed up the gain in nitrogen ceases, and the gain
in nitrate begins; sufficient may be produced to yield
corn crops so heavy as to justify the ploughing up of
pasture which is not of first rate grazing quality.

The whole chain of processes we have been describing
is of the greatest possible importance to soil fertility
because it consists in the conversion of the undecom-
posed plant residues, which are of little value to the soil
except to open it up, into valuable humus material and
plant food. The process is, in short, a release of stored-
up fertility and it has to be encouraged by every means
in the cultivator's power. It is mainly brought about by
living agencies; earthworms play a preliminary part by

46 An Account of the Soil [pi'. i

dragging the materials into the soil and effecting a
proper admixture : moulds and bacteria are the import-
ant decomposing agents. Fortunately all these organ-
isms require substantially the same soil conditions as
plants: thus they need air, water, proper temperature,
and food, absence of injurious substances, presence of
chalk, etc. The soil population is, however, very com-
plex and the organisms are not all equally useful ; there
is indeed evidence that some are distinctly detrimental.
Hitherto no method of discrimination has been adopted
and all organisms good and bad have been allowed to
grow in the soil without any intentional interference:
methods are now being worked out in horticultural
practice for controlling the soil population so as to en-
courage the useful forms and repress the others. These
methods are based on the fact that the useful forms are
less easy to kill than the others, and therefore if the soil
is heated, treated with mild poisons, dried by the sun,
or frozen for long periods during the winter, the sur-
vivors are on the whole more useful to the cultivators
than the original lot. The process is known as Partial
Sterihsation and is under investigation at Rotliamsted^.
We may now summarise the processes described in
this chapter.

1. Decomposition of plant and other proteins gives
rise to ammonia, which is then oxidised to nitrates. The
production of ammonia is called ammonification, and
the oxidation to nitrates nitrification.

2. The nitrates are taken up by growing plants and
built up into protein. Certain soil organisms can effect
the same change in presence of carbohydrates.

^ See Reports on Partial Sterilisation in the Journal of the Board of
Agriculture, 1912, 1913 and 1914.

CH. Ill]

The Soil Cycle

47

3. In absence of air some of the nitrates are reduced
to gaseous nitrogen which escapes. This process is called
denitrification.

4. A loss of nitrogen also occurs when rich soils are
cultivated. It is possible that this is also denitrification,
but the evidence is not yet sufficiently definite to justify
the use of the term.

5. The losses indicated in the two preceding para-
graphs are made good as follows. In presence of easily
oxidisable organic matter, especially of carbohydrates,
certain organisms are able to fix gaseous nitrogen and
build it up to the form of protein. This process is called
nitrogen fixation ; it must not be confused with nitrifi-
cation.

The protein formed during nitrogen fixation, however,
can undergo nitrification in the usual way, being de-
composed to form ammonia, which is then oxidised to
nitrate.

These processes form a double cycle in the soil which
may be thus expressed :

PROTEIN

Nitrogea

by denitrifying
organisms

CHAPTER IV

THE EFFECT OF CLIMATE ON THE SOIL
AND ON FERTILITY

The horticulturist working under glass can have any
soil and almost any climate he likes to pay for, but the
farmer must accept the climate as he finds it and put up
^^ith any effect it may have on the soil and on the crop ;
the best he can do is to ascertain what these effects are
and then prepare against them. It has been shown that
they fall into three groups :

1. Climate helps to make the soil and decide the
type.

2. It influences the productiveness of the soil.

3. It determines the crops that can be grown, and
hence is the final agent to decide what shall be done
with the soil.

The effect of climate in determining the general
character of the soil

Climate affects both the mineral framework of the
soil and the nature and amount of the organic matter
present.

Effect on the mineral frameicork. The origin of the
mineral framework has already been discussed and it
has been shown that two great factors determine its
composition: the composition of the original rock, and
the nature of the agencies concerned in the disintegra-
tion and decomposition. These agencies are mainly
climatic. The breaking down of the original rocks pro-

CH. iv] Effect on Mineral Matter 49

ceeds in widely different fashion in places where the
climatic conditions are very different and cases have
been observed where the differences in soil of two
regions are greater than could be expected from the
rocks alone; these differences are therefore attributed
to climate. For example, in this country the rocks
break down to yield enormous quantities of silica, the
cliief constituent of sand, and of various complex sili-
cates, containing combinations of iron and aluminium,
which occur largely in clay; iron and aluminium com-
pounds, however, form only relatively small propor-
tions of the soil. But in parts of the tropics, where the
disintegration processes have gone on under wholly
different conditions, the rocks have broken down to
yield soils containing only small amounts of silica and
relatively large quantities of aluminium and iron oxides.
These soils differ entirely from ours and have received
a special name, Laterite soils. In subtropical regions
another type of disintegration has gone on, giving rise
to considerable areas of a distinct type of red soil, in
which again there is only relatively little silica. The
study of these changes is very incomplete, and it is not
supposed that the original rocks were identical in all
cases. But it is very significant that under these three
sets of climatic conditions three distinct varieties of soil
have arisen, all differing in character and requiring
different treatment.

There is a second direction in which climate regulates
the composition of the soil. As we have already seen,
the particles formed from the rocks do not remain where
they are but get carried away by various climatic
agencies such as running water, ice, or wind. Usuallj^
there has been some selection and the particles became

R s. 4

50 An Account of the JSoil [pt. i

sorted out to some extent and suffered changes on the
journey. The amount of sorting and the extent of the
change depend largely on climatic factors.

Effect 071 the organic matter. The mass of mineral
particles formed by weathering of the rocks and sorting
out by subsequent agencies is not yet soil, although it
may be looked upon as the framework of the soil. But
it soon covers itself with vegetation which gradually
produces the remarkable results dealt with in Chapter
III and converts the mineral mass into a true soil.

The character of the soil is very much affected by the
nature of the organic matter present, and tliis is largely
determined by the type of vegetation that grows there
and the extent to which the decomposition has pro-
ceeded. Now both these are cHmatic effects. Under
dry conditions the plants tend to be narrow-leaved and
tough — e.g., pine needles, broom, etc. — whilst under
moister conditions a larger more leafy type of vegeta-
tion arises. These two types of vegetation break down
in very different manner in the soil: the large leafy
plants yield a large supply of useful humus material,
while the shrubbier and more leathery plants of the dry
situation do not. There may be plenty of organic matter
in these dry soils; the light dry sands of the Sussex
heaths sometimes contain as much as 10 per cent, but
it exists in the form of undecomposed bracken fronds
and similar residues, and is of no agricultural value be-
cause it is not properly decomposed.

Soil losses

So far we have been considering only the building up
of the soil ; we have now to turn to the other side of the
account and study the losses that are going on. The

GH. iv] Soil Losses 51

processes that called the soil into being are still opera-
tive to-day; the transport of material did not come to
an end when the soil was brought into its present
position but continues, and tends to remove the soil
now that it is formed. The losses have gone on simul-
taneously with the formation of the soil and they still
continue. The most important source is the rain. As
rain falls on to the land and soaks in, it dissolves out
some substances and carries them away. Hence the
drainage-waters are always hard and often unfit for
drinking. The constituent removed in largest quantity
is calcium carbonate, no less than 8 to 10 cwts. per acre
of this being washed away each year at Rothamsted.
Other constituents, especially nitrates, are removed in
smaller but still important amounts. Thus in course of
time a soil exposed to a heavy rainfall tends to become
reduced to hard insoluble residues of unchanged mineral
fragments : finally it may become barren through loss of
plant food, and "sour" through absence of calcium car-
bonate. On the other hand a soil in a dry region of low
rainfall keeps all its soluble constituents intact, indeed
it may become so heavily charged with them as to be-
come barren through this very excess. Again, heavy
rainfall may wash the soil bodily away and leave only
the bare rock or a wholly impossible subsoil. This some-
times happens in our own country in hilly regions: a
serious instance occurred in 1910 in the Yorkshire Wolds
north of Driffield. It is not infrequent in lands of violent
storms, especially where man has come in and removed
the native vegetation that once afforded some measure
of protection: the eroded lands of Australia and the
dongas of South Africa afford instances. Wherever some
break in the surface of the veld allows the rain to start

4—2

52 An Account of the Soil [pt. i

a little water-course, thQ washing away goes on along
that line. The break may be a natural depression, or it
may result from clearing the veld for cultivation or even
from keeping cattle always to one track in passing to
and from their drinking-places. Torrential rains soon
remove the soil and lead to the remarkable erosion
shown in Fig. 13. The remedy consists in delaying the
water and making it run off more slowly.

Soil belts and climatic zones

We have seen that right from the very commence-
ment of its history the soil has been moulded by the
climate, and it is not surprising, therefore, that parts of
the earth with characteristic climates should also have
correspondingly definite soils. Wherever there is a well-
marked climatic zone we may look for a well-marked
soil type. In classifying soils it is necessary first to
divide them into great groups according to the climate
and then to subdivide these groups according to the
geological origin of the material.

These zones can be recognised in any great continental
area. In the great dry belt in the west of North America
there is a scarcity of vegetation, consequently no great
amount of organic matter finds its way into the soil.
Further, in the absence of rain recourse is had to irriga-
tion which leads to an accumulation of soluble salta
some of which are directly harmful to the plant while
others indirectly injure it by depriving it of such little
soil moisture as is present — for plants can only take
water from weak and not from strong solutions. The
salts arise in part from the breaking up of certain
mineral particles, but in the main from pre-existing
inland seas or lagoons that have long since disappeared.

CH. lyj

Erosion by Main

53

.as ^m;«.

Fig. 13. Dongas in South Africa caused by heavy rainfall.

54 An Account of the Soil [pt. i

Soils thus charged with salts are called Alkali soils ; they
occur sometimes in patches and sometimes in great
areas, but are always dreaded alike by cultivators and
travellers. For as they dry the wind blows them up
into the eyes and mouth and nostrils till the membranes
smart again ; they carry no broad-leaved vegetation and
they yield no drinking water. Patches in cultivated
fields are marked by the failure of the plant. The soil
is curiously mottled in appearance : it forms hard white
lumps round which black water collects or dries to leave
a black crust behind. It is hard on top but often mushy
below, especially in irrigated regions, and after you have
kicked away the surface layer you come into a thick
stodgy clayey mass. Proper drainage and in certain
circumstances treatment with gypsum have done much
to reclaim these lands.

Moving eastwards and northwards there is a rather
moister belt with more grass and less alkali, but the
vegetation is still wiry or leathery and there is no
great amount of organic matter in the soil. These are
the steppe soils which can be found in parts of the
Western States and of Alberta. Alkah spots still
occur, and Fig. 14 shows one on a farm at Fremont,
Nebraska.

Still further eastwards and northwards is a zone of
higher rainfall where the conditions were such that
organic matter accumulated to a very marked extent
in the soil. Here arose the wonderful black soils on
which so much wheat is grown, especially developed in
Manitoba, Saskatchewan and Alberta, in IMinnesota and
other Middle Western States.

Elsewhere, however, the black soil is not seen, but the
loess, a wind-carried soil derived from glacial drift and

CH. IV]

Loess Soils

55

mingled with calcareous debris but without the large
amounts of organic matter of the black soils. These
give the deep rich soils found in Eastern Nebraska, Iowa
and parts of the Mississippi valley. All these areas are
characterised by cold clear winters and hot dry summers.
In the aggregate the rainfall may be sufficient but its
distribution is not always favourable to maximum crop

Fig. 14. Alkali spot, Fremont, Nebraska.

production. These areas are in the main treeless (see
Fig. 20).

Coming still further east into the regions of wood
and forest where the climatic conditions approximate
more closely to our own, the soils also resemble ours in
England.

A wholly different type of soil, known as the Tundra,
is found in the far north in the barren lands. It is black

56 An Account of the Soil [pt. i

and peat-like and the subsoil is as a rule permanently
frozen: it is covered only with mosses, lichens, etc. and
lies beyond the regions of our accustomed vegetation.

Any other continental area can similarly be divided
into zones corresponding broadly with cHmatic zones.
In Russia, for example, white desert soils poor in organic
matter but often containing alkali are to be found in the
dry Caucasian region: further north under a limited
rainfall of 8-12 inches occur the brown steppe soils,
their deeper colour indicating their higher content of
organic matter; pushing still further north a belt of
chestnut coloured soils is found stretching away in a
north-easterly direction from Podolia in the south-west
across Little Russia to Samara and Orenburg in the east.
Above this again comes the famous belt of black earth,
the Tchernozem, the nearest European approach to the
black soils of the western prairies and like them devoted
largely to the cultivation of wheat; these are found in
Hungary and continue north-easterly through the west
Russian province Volhynia to the Government of Perm.
Further north these are succeeded by the Podsols, white,
poor, acid soils in a cold wet belt still left in forest ; and
finally above them come the Tundra soils, acid, treeless,
carrying only lichens and moss.

Even in England indications of climatic zones can be
traced, although in the main our soils would fall into
one great group of woodland origin. But in the dry
eastern counties some of the heaths are distinctly steppe-
like in character, while in the wet high-ljdng districts of
the north and west occur moorland soils entirely
different from the clays, loams and sands of the mid-
lands and the south.

CH. iv] Weather 57

The effect of iveather on the soil

While climate plays a great part in determining the
general character of the soil the weather is responsible
for tolerably wide variations exhibited from year to
year.

There are at least five ways in which the weather or
seasonal effects operate:

1. High rainfall tends to wash out two very useful
constituents, calcium carbonate and nitrates, both of
which must be replaced or the soil loses fertility. For-
tunately other useful substances are absorbed by the
soil and are therefore less liable to be lost.

2. High rainfall has an adverse physical effect and
spoils the tilth.

3. In dry conditions there is less or no washing out
of calcium carbonate or of nitrates, and hence less
wastage of fertility.

4. Drought, frost, hot sunshine, and other factors
which are detrimental to plant life are finally beneficial
to bacterial activity (p. 46), and lead to an increased
production of plant food.

5. Frost has a beneficial effect on tilth.

These factors of course all intermingle in their action,
but their general effects may be summed up briefly.

The nitrates formed during spring and summer by
bacterial action, and destined to serve as food for the
next generation of plants, are readily washed out during
a wet winter, but they remain safely locked up in the
soil throughout a period of frost and snow when no
leaching takes place. There they lie ready for use when
spring awakens the young plant into activity; conse-
quently a mild spring following on a hard winter is

58 An Account of the Soil [pt. i

commonly a period of \dgorous growth. Tliis is well
seen in Canada, where a remarkable development of
vegetation takes place directly the weather is sufficiently
warm. In part the result is due to the effectual cold
storage of the plant food, neither loss nor deterioration
going on in frozen ground, in part also to the increased
activity already mentioned of the food-making bacteria
after a spell of adverse conditions.

Another effect of a wholly different nature is also
produced. Frost puffs up or lightens the soil: it splits
the hard clods and brings them down to a nice crumbly
tilth well adapted for a seed bed. Further, it tends to
change clay from the sticky into the crumbly state. On
the other hand long continued wetness has the opposite
effect : it consolidates the soil, makes it sticky and very
unsuitable for seeds. Thus at the end of a mild wet
winter the soil is poor in plant food because of the
leaching that has gone on, its population of micro-
organisms is not highly efficient in making food, and it
is in a bad mechanical condition because the wetness
has made the clay particles very sticky. On the other
hand at the end of a more severe winter when the land
lay frostbomid or covered with snow there is a good
supply of plant food, all the autumn reserves having
been safely locked up in the soil, the micro-organic
population has become more efficient in producing plant
food through the partial suppression of detrimental
organisms, the texture of the soil is very favourable for
the production of a good seed bed. The advantages,
therefore, are wholly in favour of a dry cold \Wnter, and
we can see the wisdom of the old proverbs :

"Under water famine, under snow bread,"
"A snow year is a rich year,"

CH. iv] Effects of Frost and of Sunshine 59

and of the more recent calculation by Sir W. N. Shaw
that every inch of rain falling during the autumn
months — September, October, and November — blowers
, the yield of wheat during the next season in the eastern
counties by a little over 2 bushels per acre (2*2 to be
precise) from an ideal standard of 46 bushels per acre.

The older writers, noticing the value of frost and
snow, thought they had an actual fertilising value, and
indeed many gardeners and farmers will still contend
that snow is a manure. Opinions of good cultivators are
always entitled to respectful consideration, and many
analyses of snow have been made, but they have failed
to reveal any appreciable amount of fertilising con-
stituents. Snow differs a little from frost in its action:
it forms a non-conducting coat for the soil and prevents
the temperature from falling as low as it otherwise
would. Any plants that happen to be in the soil benefit
by the snow cover because their roots are protected from
excessive cold.

A hot dry summer has at least as beneficial an effect
on the soil as a cold dry winter. The drying out cer-
tainly changes a heavy soil into clods, but when these
are moistened again by autumn rains they readily fall
to a good tilth. If the warmth has been sufficient there
is an even more marked improvement in the soil popu-
lation as far as food-making is concerned than after a
cold winter.

The effect of season on the nitrate content of the soil.
The manufacture of nitrates in the soil (which, as we
have seen, is an indispensable process for the welfare
of the crop) takes place most rapidly in our climate in
late spring or early summer. It then slackens down
while the plant is growing, but it may speed up again

60

An Account of the Soil

[PT. I

in a warm moist autumn. Typical results are shown in
the curve of Fig. 15. In a dry summer the nitrate
formed is all left in the soil or taken by the crop : in a
wet summer some of it is washed out. This is shown
by comparing the amounts of nitrate present on an un-
manured fallow plot at Rothamsted during the wet
summer and autumn of 1912 with those present in the
dry summer of 1 9 13 . In the top 1 8 inches of soil amounts
were found equivalent to the following quantities of
nitrate of soda, in lbs. per acre, showing a very great
difference in favour of a dry summer :

Feb.

May

Sept.

Dry summer, 1913 126

312

376

Wet summer, 1912 180

138

114

T\» nr

ce in favour of dry summer

Differen

reckoned as nitrate of soda

174

262 lbs. pe

l-<

^^— '^3X

o3 _•

20

y""^^ \

oT "»

/ \

-iiS «4-l

eS O

/ X

-fe C

/ \

x*^ X

•2;§

ai -5

10

/ \

\

* a

\

c .

o ^

^S.

Lri

-4^

»5

March Apl. May June July Aug. Sept.

Fig. 15. Curve showing average amounts of nitrate present in
cropped soils at different seasons of the year. (Rothamsted.)

The nitrates left in the soil at the end of September
represent the initial stock for the farmer during the
coming season. After a dry summer it is high, after a
wet one low. How much of it ever gets into the crop
depends on the winter weather. A wet winter will wash
much of it out while a dry winter conserves it safely.

CH. iv] Losses of Nitrate 61

During the wet winter of 1911-12 the following losses
took place from some micropped soils at Rothamsted
and Ridgmont:

Loam in Poor

good heart loam Clay Sand

Rothamsted Rothamsted Ridgmont Milbrook

Present in Sept. 1911 690 306 234 102

Remaining in Feb. 1912 186 168 180 54

Lost during winter 504 138 54 48

Reckoned as lbs. of nitrate of soda in top 18 ins. per acre.

The loss from sand is small because the stock happens
to be low, and from clay it is also small because percola-
tion of water does not readily take place. The most
serious losses are from good loams. In dry winters the
loss is less, but on an average the loam at Rothamsted
loses during winter months as much nitrate as would be
required by a 4 quarter wheat crop.

If the student has access to drainage -water from
a field he should make the following experiments
periodically :

( 1 ) Test for nitrate and compare with a standard solu-
tion to ascertain approximately the concentration (p . 2 2 8 ) .

(2) Test for calcium. In many cases so much calcium
bicarbonate is present that a precipitate is thrown down
on warming the solution.

The following experiment shows how a crop affects
the drainage.

Take two glazed tubulated pots (Doulton's "mixing
jars" shown in Fig. 1), fill with soil, keep one pot fallow,
sow grass-seed in the other. Fit the tubulure with a
tight cork through which passes a glass tube bent so as
to deliver the drainage-water into a bottle. Measure the
amount of drainage after rain and estimate the nitrate
present. The experiment must run over the whole

62 An Account of the Soil [pt. i

season ; in a period of drought rain-water may be gently
supplied from a water-can, although it is hardly possible
to simulate the action of rain itself.

Fig. IG. The drain gauges, Rothamsted, used for studying the
amount and composition of drainage-water.

The gauges used at Rothamsted for studying drainage
problems are shown in Fig. 16.

The various bad effects of wet weather are reflected

CH. iv] Practical Remedies 63

in the crop. A wet winter is notoriously bad for the
wheat crop; on the other hand a dry winter is much
more favourable. Shelter of course is just as effective
as dryness: the ground where a stack has stood over
winter is well known to be more productive than ad-
joining ground that has been exposed to the rain.

The practical point arises: how can the cultivator
remedy matters? He must try both prevention and
cure. Loss of nitrate can be prevented by sowing catch
crops 1 in autumn to be ploughed in or folded before the
spring sowings (p. 114). Bad tilth can be diminished by
leaving the ploughed land rough and taking care that
the wheat land does not get too fine. If the soil is already
fine, as, for instance, it is left after potatoes when the
digger has thrown down the ridges, the wheat seed can
advantageously be broadcasted or drilled on the surface
and then ploughed in and harrowed, thus exposing a
new and rougher surface to the weather.

Loss of nitrate can be made good by spring dressings
of quick-acting nitrogenous manures : soot or sulphate of
ammonia if the surface is sticky, or nitrate of soda if the
soil can be got into reasonable condition (Chapter VII).
Finally the bad effect on the surface can be remedied by
using the Crosskill or other roller when the land is dry,
following this with the harrow.

The effect of climate in determining what crops
can he grown

The fertility of a soil is judged by its power of pro-
ducing crops, but it obviously cannot grow crops unless
the climate allows: we therefore have to turn to the

^ Particulars of suitable crops are given in the Food Production
Leaflet 51, Board of Agriculture.

64 An Account of the Soil [pt. i

effect of climate in deciding what crops can and what
cannot be grown. There is a fairly simple connection
between the type of crop and the climate. In general
seed does not ripen well in wet seasons or districts, and
crops wanted for the sake of the seed are usually grown
in dry rather than wet districts. On the other hand
actual plant growth, i.e., growth of leaves, stems, and
roots, is much better in moist than in dry districts or
seasons. For example, the abnormally dry summer of
1911 was excellent for grain crops so that the corn was
uncommonly good, but it was so disastrous for the
growth of grass that hay went up to two or three times
the price obtained in the previous season. The wet
summer of 1909 was very favourable to the growth of
grass, swedes, etc., but bad for the production of seed.
Another factor also comes into play. Very wet land
cannot easily be dug or cultivated : if it is to be used for
agriculture in these days of high costs all cultivation
must be reduced to a minimum. Now the crop that
requires least cultivation is grass ; it is accordingly very
much grown in wet districts. Since grass has to be used
by animals of some sort a good deal of live stock is
usually kept either for the production of meat, butter,
cheese, etc., or for breeding j^'oung animals to be sold to
other districts. Wherever cultivation becomes expensive
for any reason there is a tendency to resort to grass and
pastoral conditions.

The following rules will be found useful in discussing
crop production in temperate regions; they are, how-
ever, by no means absolute. Warm districts yield early
crops, and are therefore well adapted for market garden
produce and for fruit. Moderately dry regions are
suited for seed crops. Moist er regions are adapted for

CH. iv] Distribution of Crops 65

seed crops that need not fully ripen such as oats, for
root crops like mangolds, swedes or potatoes, or for leaf
crops like the cabbage tribe. Wet regions are commonly
devoted to grass.

Fig. 17 shows the distribution of rainfall in England
and Wales: Fig. 18 shows the distribution of wheat and
Fig. 19 that of grass. It will be observed that wheat-
growing tends to concentrate in the drier eastern parts
of England and grass-growing in the moister west and
north.

The factors that determine the regional distribution
of crops operate everyAvhere and many illustrations
of their action may be found within very restricted
areas.

Land lying at the bottom of a slope is moister than
land lying higher up, because it receives the water that
has drained down from above as well as its own share
of the rainfall. Sometimes it is so wet that it forms a
marsh unsuited for cultivation and therefore left in
grass; the land immediately above is then commonly
used for general crops. But where the water level is well
below the surface of the soil the bottom land is not
marshj'- but is on the contrary highly fertile and is more
regularly supplied with water than the higher land.
Land at the top of a slope may be too exposed or too
cold for cultivation, and often if it lies above 700 ft. in
England it is left either as grass, wood or waste; the
limit is higher in places, e.g., the milder parts of Wales,
Cornwall, the Yorksliire Wolds, etc.

The following is the typical sequence in travelling up
a valley or a slope in England. If the bottom is marshy,
grass only is grown there ; if it is dry, good crops of roots,
cereals or other plants can be obtained ; higher up arable

K. s. 6

66

An account of the Soil

LiT. I

Inches
Over 60

j^agll 50 to 60

30 to 50
25 to 30

Under 25

Fig 17. Annual Rainfall in England and Wales. For a detailed discussion see
H. R. Mill and C. Salt r. Jo rn. Roiial Mrteoroloj. Soc. 1915, Vol. 41, p. 1.

CH. IV]

Wheat

67

Over 20%

10 to 20%

Fig. 18 Percentage of Cultivated Land in Wheat, 1915.

Figures from Agricultural Statistics, Vol. L, Pt. 1, 1915.

Acreage and Livestock Returns.

68

A)i Acconuf of the JSoil

[pr. I

Fig. 19. Percentage of Cultivated Land in Grass, 1013.

Figures from Agricult)ind Slatisiici'. Vol. L. Pt. 1. lStl5.

Acreage and Livi'j^toek Rt'turns.

CH. ivj Late Frosts 69

crops are grown or, as we shall soon see, fruit; still
higher comes grass land, especially in the cold north,
while above the 600 or 700 ft. contour is wood or waste
land.

The small difference in temperature between a north
and a south slope may have a considerable effect on the
crop, vegetation on a south slope being a little more
forward and ready for market before that on the north.
In ordinary agricultural practice this is not usually of
much importance but it is for market garden work;
amazing differences in price are often attached to small
differences in time of marketing.

More important, however, than high mean tempera-
ture is the absence of spring or autumn frosts. Low
lying valley lands are peculiarly susceptible to frosts on
clear calm nights; the cold air drifts down from above
and collects in the valley where it chills the trees and
not infrequently kills the fruit blossom and the tender
shoots of early potatoes. Land lying above this stagnant
pool of cold air escapes these frosts and is therefore a
safer place for susceptible crops, even though its mean
temperature may be lower than that of the valley.
Where, however, the low land adjoins the sea or any
great body of water it is protected from these frosts and
is, indeed, better than land Ijing further off because it
is warmer.

We can now understand why fruit is so often grown
in undulating country. Slopes are needed to give the
desired shelter and aspect, but above all to avoid risks
of late frosts. The "lucky banks" of the Evesham
district, on which crops can nearly always be got, are
of this character. In the fruit-growing region of Kent
the fruit tends to collect on the middle slopes, hops on

70 An Account of the Soil [pt. i

the lower ground (or wood, if the ground is wet), and
woodland or nuts on the higher ground. But near the
sea — and this holds generally round the coast — fruit can
be grown with advantage on the lower ground.

Climate and soil, however, do not entirely determine
what crops shall be grown, although they certainly play
a great part. Agriculture is always pursued for profit,
and the cultivator does not necessarily go in for the crop
that naturally grows best on the land, but the one that
pays best. Thus a set of economic factors comes into
play, working along with the climatic factors and with
them determining what crops shall and what shall not
be grown. It is impossible to overlook these economic
considerations in any real study of soil fertility, but as
we must keep our subject within reasonable bounds we
can only indicate their general nature.

As the produce of the land has to be sold it obviously
must be got to the market; chief among the economic
factors is therefore the question of transport. From
this point of view live stock presents least difficulties;
animals can be made to walk to market while crops have
to be carried. Sheep, cattle, and horses therefore tend to
become the mainstay of agriculture in countries desti-
tute of transport facilities. But where transport is
possible wheat or maize becomes the most convenient
product, for either will keep almost indefinitely so long
as it remains dry, suffering little if any deterioration,
however long the journey to market may take, and,
what is more important from the settler's point of view,
both are always saleable. On the other hand, fruit and
vegetables will not keep and can only be grown where
transport facilities are good.

History repeats itself with but little variation in the

CH. IV]

Prairie development

71

Treeless prairie, first stage of development.
Ranching (Sounding Lake, Alta.).

Treeless prairie, last stage of development. An Experimental
Farm (Indian Head, Sask.).

Fig. 20. Development of prairie land, Western Canada.

72 An Account of the Soil [pt. i

agricultural development of virgin countries in temper-
ate regions. At first the country is pastoral. Then with
the opening of railways comes wheat or maize produc-
tion. Later on when the country is more closely settled
other crops are raised and wheat loses its premier
position: oats are wanted in enormous quantities for
the horses used in railway and other construction work,
green crops are needed for the cattle and sheep, and
other crops are wanted to satisfy the more exacting
needs of the population that follows the simple-living
pioneer. Then as transport becomes still easier fruit and
vegetables are raised in suitable districts for shipment
to the cities or abroad (Fig. 20). Canada, South Africa,
Australia and the United States show all these stages of
development. Finally, when wealth has accumulated
and brought leisure and freedom from the struggle,
there arises a fastidious people that picks and chooses
and puts a price on subtle differences in qualit}' in-
appreciable to the unsophisticated. Fashion, prejudice
and sheer boredom now become factors and lead to
demands for particular varieties of particular crops
grown in some special manner: so high a price is offered
to anyone who will provide these things that the supply
is soon forthcoming.

The position to which all these observations lead is
this: climatic considerations dictate what crops can and
what cannot be grown in a given region; they further
modify the soil and thus affect the ease of raising the
crop. Economic considerations such as transport and
market price determine which of all possible crops shall
actually be grown. All this leads to much specialisation
in crop production as is demonstrated by the crop map
of Great Britain (Fig. 21). The warm districts of Corn-

CH. IV]

The Crop Map

73

wall, the Channel Islands and parts of the Ayrshire
coast ;\deld early crops; the dry districts of the eastern

anJ Cabbage _"
CaylifiowiTs

Fig. 21. Crop Map and Isotherms of Great Britain.

counties produce wheat, barley, peas and seeds. The
cooler moister regions of Cheshire, the Fens, the Wash,

74 An Account of tlie Soil [pt. i

and the Lothians produce potatoes ; oats and swedes are
raised in moist regions, while in still wetter districts
grass and dairying come in. Wherever the climate is
satisfactory and the railway connections good an in-
dustry springs up in fruit and vegetables. Finally, the
higher or less accessible districts are given up to the
raising ot live stock to be fattened out in those favoured
districts where animal food grows more quickly than the
animals bom on the spot can consume it.

To some extent it is possible to modify the dominating
effects of climate on crops ; there is a little elasticity in
both directions. Plants are somewhat plastic and can
be moulded to a certain degree in the plant breeder's
hands ; they can be bred to tolerate greater cold or more
drought than usual. Thus in Canada wheats are being
produced to grow further north than ordinary kinds so
as to take into cultivation a belt of land at present
suited only for grass. In Australia wheat has been bred
to tolerate drought and grow in the drier regions. This
sort of work is being done very widely and we do not
yet know how far it can be pushed.

Climate apparently cannot be altered; indeed, we can
only get over some of its bad effects in one direction.
Temperature is at present beyond our control; the hot
regions remain hot and the cold regions remain cold and
we camiot alter matters. Wet districts can be improved
somewhat by drainage. Our great triumph, however, is
in the dry districts. Irrigation and the special agri-
cultural methods known as dry farming have brought
into cultivation enormous tracts of land, hitherto desert,
in India, South Africa, Canada, Australia and Egypt,
while a great project is on foot for Mesopotamia. But
the mention of Egypt and of Mesopotamia reminds us

CH. iv] Old and New Methods 75

that our modern triumph is no modern invention. Egypt
and Mesopotamia were irrigated long before our civihsa-
tion appeared; the farming methods of the Syrian
peasant handed down by long tradition contain in them
all the principles of our modern dry farming-;!.

1 "Dry farming in Syria," J. Agric. West Australia, 1908, xvi, 206.

PART II

THE CONTKOL OF THE SOIL
CHAPTER V

CULTIVATION

Ix the preceding chapters we have been dealing with
the soil as it stands in the field and studying the changes
which it undergoes in the natural state. We now turn to
the second part of our subject : the methods whereby the
farmer can utilise the soil to the greatest advantage and
make it yield crops in quantities that repa^^ the time and
trouble involved.

Two courses are open to the farmer: he may be con-
tent with the soil as it is, or he may try to improve it.
The first is much the simpler plan and has perforce to be
adopted in many parts of the colonies : the improvement
of the soil is a more serious affair, and is looked upon as
being in part at any rate the landlord's business. The
distinction is so important in practice that special terms
are used to express it. The word " heart " or " condition"
denotes the state of the soil as it stands ; a soil being m
good "heart" when the farmer is working it for all it is
worth, cultivating and manuring it wisely and well but
not effecting any costly improvements. "Fertility" is
used to express the inherent capabilities of the soil
which can only be improved by costly operations usually

CH. v] Condition and Tilth 77

undertaken by the owner of the land. The distinction
is not as real as it looks, "condition" and "fertility"
are simply different degrees of the same thing, and they
are separated only as a matter of convenience. In this
chapter we shall deal with the simpler case only, and
shall discuss the cultivation processes which make full
use of everything in the soil without, however, per-
manently improving it.

Practical growers have long since discovered that
crops will not grow unless the land is properly culti-
vated, and indeed the connection between cultivation
and crop growth is so close that much of the improve-
ment in farming in the last century must be put down
to iniproved methods of cultivation, while much of
the success of the best farmers in growing large and
vigorous crops to-day arises from the complete mastery
they have gained of the cultivation of the soil. Winter
and spring work on the land consists largely in the
preparation of the seed bed, and unless this is properly
done the crop runs great risk of failure.

The first object of cultivation is to get the soil into a
good "tilth," i.e., to make it assume the nice crumbly
condition which long experience has shown is best suited
to the growth of plants. The important fact here is that
the clay can exist in two states — the sticky and the
crumbly state (p. 21): and it is such a dominating sub-
stance that it confers these properties on the soil. In
consequence any soil which contains more than about
10 per cent, of clay may appear in two very different
guises — either in the nice crumbly condition of a fine
tilth, or in the other state when it is sticky after a spell
of wet weather, and dries into hard clods in dry weather.

The second object of cultivation is to free the land of

78 The Control of the Soil [pt. ii

weeds, which has to be done by uprooting them and
leaving them on the surface to perish for want of water,
or, in the case of annuals, burying them deeply enough
to prevent their springing up. Weed seeds unfortunately
cannot be killed in this way, but must be encouraged to
germinate; the young seedlings are then uprooted. This
process is called "cleaning" the land.

Winter cultivation . As soon as possible after the com
is cut, and if necessary before it is carted, a broadshare
should be sent over the land to skim off the surface and
leave it to dry. Weeds and grass are thus killed, but the
ground below remains moist enough to afford weed
seeds a chance of germinating. Winter ploughing can
then be begun when convenient.

On heavy lands the earlier this is done the better.
The special objects here are to ensure that the land shall
dry quickly in spring and that the clay shall take on
the proper crumbly condition. The former is secured
by leaving the land in a rough state so that a consider-
able surface is exposed, and also by arranging that water
can easily get away. The latter is effected by a combina-
tion of good cultivation with the addition of lime, chalk
or limestone, and of organic matter, and by exposure to
frost. On the other hand long exposure to water {e.g., a
long wet winter), alkaline substances such as liquid
manure, large excess of certain fertilisers, and general
bad management, all tend to change the crumbly into
the undesirable sticky state.

On light, sandy or peaty land it is not necessary to
start so soon : the main object is to kill weeds, and delay
is permissible so long as no seeding takes place.

The process of cultivation is carried out first by
ploughing, then by harrowing and rolling. It is not our

CH. v] Ploughing 79

business to discuss types of implements, but we must
deal to some extent with the kind of work thev do.

The plough consists essentially of two cutting edges,
a vertical one called the coulter and a horizontal one
called the share, and a curved steel or iron plate called
the mould board which turns over the slice of earth as
it is cut. The traditional English style of ploughing is to
turn the slice without breaking it, so as to form a
succession of parallel ribbon-Kke strips over the whole
field. On light soils the slice is turned right over so that
the surface remains pretty level: thus the surface weeds
are buried, and the seeds below the surface have a chance
of germinating. On heavier soils, however, while the
vegetation is still ploughed in, the slice is left on edge
with high crests so as to expose more surface and to aUow
more complete penetration of frost and at seeding time
a better entrance to the tynes of the harrow.

In the middle of last century the mould board was
modified by the American makers so as to break the
slice as it turned over^ : these ploughs were subsequently
called "digger" ploughs or Oliver ploughs from a
successful maker in the 'eighties. The work done is not
so nice looking as in the old English style, but it is
probably more effective excepting in a wet season when
the surface is liable to be beaten down too much. These
different types of furrow-slices are shown in Eig. 22.

A team of horses can plough three-quarters of an acre
to one acre per day on heavy land in England; how-
ever urgent the need they can hardly do more. It is
obvious therefore that a wet autumn and winter gravely

^ See an interesting Report in the Transactions of the New York State
Agric. Soc. 1867, p. 386. For a more recent investigation see E. A. White,
Journ. Agric. Research, 1918, xii, 149-182.

80

Tlic Control of the Soil

[PT. II

Fig 22. Types of furrow slices.
1. Rectangular unbroken. 2. Crested. 3. Rectangular broken.

CH. v] Importance of Good Ploughing 81

handicaps the farmer and leaves him with his work
sadly behindhand in spring. This handicap will, it is
hoped, be removed with the further development of the
motor or tractor plough : the farmer will then be able to
take full advantage of every favourable interval and
have his ploughing carried out in time.

It is usual in some districts to plough to the same
depth every year. This is not desirable as the plough
sole tends to compact the subsoil and form a hard layer
which roots cannot penetrate. It is advisable one year
in four or five to plough to a greater depth so as to get
underneath this layer: this deeper ploughing can well be
done for roots or potatoes.

It is impossible to overestimate the importance of good
ploughing. Winter sown corn is specially dependant on
it. In the old days farmers hked to have an interval be-
tween the plougliing and the sowing of winter wheat, or
in their own words to sow " on a stale furrow." Modern
ploughs do better work, and good results are obtained by
sowing straightway after ploughing on a "fresh furrow."

In some parts of the country, e.g., in parts of Wales,
farmers tend to use a quicker method and scarify their
land instead of ploughing it. This is not desirable.
Scarifying does not clean the land as thoroughly as good
ploughing, and it is by no means an efficient substitute^.

The time at which ploughing is done is a very impor-
tant matter. Once the land is ploughed it not only ceases
for the time being to carry a crop, but it is more exposed
to the washing action of rain, which may mean con-

^ Some striking American experiments on the effects of good and bad
ploughing, deep and shallow ploughing, etc., are recorded in Hosier and
Gustafson's book. Soil Physics and Mmiagement, Chap, xxvi, and also in
the Kansas Bull. 185.

R. s. 6

82 The Control of the Soil [pt. ii

siderable loss of plant food. A soil that is at all light or
porous readily loses its valuable nitrates, and although
the loss is not so serious on heavier loams and clays, it
takes place even there. The loss only goes on, however,
in wet weather, and if one could rely on having the
ground frozen hard throughout the winter it would be
simple enough to arrange about cultivation; one would
turn the ground up roughly at the beginning of the
winter, and leave it to the end. Unfortunately our
winters are variable: land turned up in autumn may
only occasionally get frozen, and may lie wet for long
periods ; it then derives very little benefit from the culti-
vation, and suffers considerable loss of plant food.

It must, therefore, be arranged that the cultivation
effect is at a maximum, while the loss is at a minimum.
The general rule is that light soils may be left unculti-
vated until late in the winter or early spring, partly
because the amount of frost they require is only small,
partly because the loss that they would suffer in rain is
very large. Heavy soils, however, should be turned up
as early in the autumn as possible because they require
a large amount of frost, and suffer only little loss. The
rule, of course, requires intelligent application and
adaptation to each locality.

The effect of winter cultivation in lightening the soil
is well seen in the following experiment devised by
Mr F. J. Gurney. Mark out a plot of groimd one rod
square and divide it up into square yards ; at the corner
of each square dig a hole 12 inches deep. Place a brick
at the bottom of each hole and on it stand an iron rod
16 inches long (and therefore projecting 8 inches above
the surface of the soil) and put in sufficient concrete to
hold the rod rigid : then fill up with earth. The plot will

CH. V]

A Cultivation Experiment

83

now be provided with 25 fixed posts projecting from the
soil (Fig. 23). Lay a straight-edge from post to post
and measure with a ruler the depth of the surface below
it. The posts being fixed this straight-edge constitutes
a fixed base line from which the change in level of the

i

1

1

i

Fig. 23. Plot of land witH fixed pegs for cultivation
experiments. (Mr Gumey's experiment.)

soil can be determined at any time. Divide the plot into
two parts, leave one alone and dig the other deeply,
leaving the surface approximately level. The following
are some of the results obtained :

Mean
62 inches

3-^ :,

Level of soil below straight-edge

Before digging 6^ o| 6| 7 7 7

After digging 4 3 3 3 3 4

Raising of surface due to digging

Readings should also be taken after a heavy down-
pour of rain, and after a good frost to show how these
affect the soil.

Spring jultivation. The object of the spring cultiva-
tion is to complete the winter cultivation and obtain
a tilth ouitable to the crop. The operations depend on

84 The Control of the Soil [pt. ii

the fact that if the clay is in the proper state small lumps
of soil readily fall to pieces when just sufficiently moist.
Hence after winter the soil is allowed to dry and is then
broken down into small lumps by a clod-crusher : these
are then allowed to become moist so that they break to
pieces with harrows. The operation probably demands
more skill and judgment than any other part of soil
management: both the drymg and the re wetting are
done by the weather and are therefore largely out of
farmers' control; only a limited time is available and
the season for sowing the crop soon passes ; and, on the
other hand, if the farmer tries to hurry matters too
much and begins before the land is dry enough he may
poach it so badly as to ruin it for a time. His only
chance, therefore, is to have his work well forward in
autumn and winter so as to take full advantage of
favourable opportunities in spring. The ideal case arises
when the soil was turned up roughly in autumn, when
the winter was frosty, and the spring just sufficiently
showery to soften the lumps at the proper time and
facilitate their breaking down under the harrows. A
mild winter makes matters more difficult because the
clay does not flocculate. If the early spring is dry the
soil dries to a hard surface, or, in the case of lighter soils,
to steely lumps which can be broken by the Crosskill or
other roller; if, however, the spring remains dry there is
great difficulty in getting any further and obtaining a
proper tilth; this is often experienced on the loams of
the south-eastern parts of England where spring rain-
fall is low and winters are mild. A good cultivator
watching his opportunities often achieves remarkable
results, but no one has yet succeeded in reducing his art
to an exact science.

CH. v] Spring Cultivations 85

The most difficult case arises when the winter is mild
and wet and the spring wpt so that the soil never dries
for the preliminary breaking down into small lumps.
The heavier the soil the worse the trouble : and seasons
of this kind have sometimes proved disastrous. No way
round the difficulty is yet known, and this is one reason
why heavy soils are often not brought into arable
cultivation.

The disk harrow is very useful in spring in mitigating
these effects and in putting right the bad work some-
times done by motor or tractor ploughs. The tilth pro-
duced may look better than it really is: "forced" tilths
are not much in favour with farmers.

Rolling. It has already been stated that frost puffs
up and lightens the soil and where the soil is already
rather porous the effect may be actually harmful to the
plant. It is essential that sufficiently close contact
should be maintained between the soil and the root,
otherwise the plant does not obtain the proper supply
of water and nutrient salts ; wherever the winter frosts
have so puffed up the soil as to reduce this contact too
much it is necessary to compact the soil again by rolling.
These effects are produced by the furrow presser used
for cereal crops on light chalky soils, and for wheat after
a ley on many other soils.

Another factor comes into play on grass land. Earth-
worms burrow in the soil and throw out material from
below on to the surface. These casts accumulate steadily
at a rate calculated by Darwin to be about one inch in
ten years. The worms honeycomb the ground with
their burrows, and this action, though necessary to the
plant, becomes after a certain stage harmful and injures
the grass while allowing moss to grow.

86 The Control of the Soil [pt. ii

Fortunately the remedy in both cases is simple : the
ground should be rolled during dry weather in spring
until the proper degree of compactness is reached. This
operation is very necessary on chalk soils, sandy loams,
and grass land.

Rolling is also necessary for corn crops on heavy land
in spring to break the crust formed after a spell of wet
weather. Great judgment is needed to decide whether
rolling or harrow ing is the better operation to perform :
a mistake in either direction may cause much harm.

Summer cultivation consists in hoeing and its object
is two-fold : to keep the surface of the soil in a fine state
and to kill weeds. A layer or "mulch" of fine soil keeps
the land cool during hot weather and prevents loss of
moisture. This was shown thirty years ago by the
American investigators, Kedzie of Michigan and King
of Wisconsin^, and is demonstrated by the following
experiment :

Set out three plots each 3 ft. x 3 ft. : leave one alone
entirely so that it may cover itself with weeds : keep the
second clean bv hand weeding but do not touch it other-
wise: keep the third well hoed. Take readings of the
temperature of the soil at depths of \ inch, 3 inches and
6 inches below the surface : in particular obtain readings
on hot sunny days and on cold sunless days. Periodically
also take samples for the determination of the moisture
content: this is done by driving in the borer (Fig. 41,
p. 227) to a depth of 6 inches, weighing the soil that is
Avithdrawn (or a fair sample of it), leaving to dry in a
warm place and then weighing again. Table II gives
some of the results which have been obtained.

^ See Kedzie, in Michigan Agric. Coll. Rpt. 1889, and F. H. King,
Wisconsin Agric. Expt. Station Rpt. 1889.

CH. V]

Effect of Hoeing

87

Table II. Effect of hoeing on moisture content and
temperature of soil^

Hot sunny day

Cold sunless day

Untouched Hoed

Untouched

Hoed

Soil temperature h"

o//

» „ 6"

35°-0 C.
30°-5 C.
27°-0 C.

31°-5C.

28°-8 C.
26°-5 C.

17°-5 C.
16°-7 C.
15°-8 C.

17°-0C.
16°-3 C.
15°-5 C.

Soil moisture, per
cent.

14-7

160

19-3

18-4

Hoeing reduces the temperature and economises the
water supply of the soil on hot sunny days, but it seems
to have no such effect in cold sunless weather.

In our country it is doubtful whether constant hoeing
would be worth doing on a farm for the sake of saving
water. In experiments in Illinois there was no advan-
tage in systematic hoeing, nor was there in some of the
other States^. But in drier climates the gains in soil
moisture are more pronounced : it is customary to send
out the disk harrows and start surface cultivation
directly a shower of rain has fallen, and before the land
has had time to dry up again. This is the central idea
of "dry farming."

Under moister and cooler climatic conditions probably
the chief effect of hoeing is to keep down weeds. This is
indicated by an interesting experiment that has several
times been made, but not with sufficient exactness in
this country, in which a crop is grown (a) without any

^ For another illustration see Cockle Park Bulletin, No. 26, 1917, p. 84.
^ See Illinois Bulletin, No. 181, p. 582; also U.S. Dept. of Agric. Bureau
of Plant Industry Bulletin, No. 257.

88 The Control of the Soil [pt. ii

hoeing or attention; {b) not systematically hoed, but
weeds scraped off; (c) hoed. The neglected plot becomes
infested with weeds and the crop does very badly, bnt
there is usually not much difference between the hoed
plot and the one where the weeds were simply pulled
out^. The student should try the experiment for him-
self. The result is very important; some of the older
soil workers thought that the actual stirring of the soil
was beneficial, but if wider experience showed that the
only effect was to kill weeds an important piece of know-
ledge would have been gained.

Cultivated plants cannot usually survive competition ;
weeds therefore have to be excluded as much as possible.
Dr Brenchley^ has shown that the weed also suffers
from the competition of the crop. From the farmer's
point of view the most important consideration is to
Idll the weed : the most effective way of doing this is by
cultivation. The best farmers always have their land
cleanest, and not only do they secure bigger crops and
higher quality but they have nothing to waste.

Earthing up. Some crops are greatly benefited by
drawing the earth up to them so as to form a ridge.
Potatoes in particular make better growth: special
implements have therefore been devised to mould them
up. The effect is complex : the process affords a thorough
hoeing, it provides more surface soil for the plant and it
encourages root formation.

In China and Manchuria wheat is grown in this way.
The method was introduced into Europe by Demtschin-
sky and tested in France: it gave largely increased

* E.g. at the Utah Agric. Expt. Station the results are aUke (Journal
of Agric. Research, 1917, x. 113-155): so at Illinois (Bxdleiin, No. 181).
2 New Phytologist, 1917, xvi. 53-76,

CH. v] Falloivimj 89

yields per plant, but proved less effective per acre than
the ordinary methods.

Ridging. In the northern counties and in Scotland it
is customary to lay the land in ridges on which turnips
or swedes are grown. The process is found to be helpful
because it facilitates drainage and evaporation; but
there is no advantage in doing this in the south, where
there is usually too little rather than too much water.
Trials made in Essex showed that mangolds grew better
on the flat than on ridges^.

Fallowing, or leaving the ground free of crops, gives
the farmer a free hand for his cultivations, and much
increases the stock of nitrate in the soil: the growing
plant apparently interferes with bacterial activity and
reduces the amount of nitrate produced. Thus there is
less nitrate present on cropped land than on fallow land
even after allowing for what has been taken up by the
crop. The following data were obtained at Rothamsted :

N as nitrate, lbs per acre

June 1911

June 1912

fallow

wheat

fallow

wheat

In soil ...

54

15

46

13

In crop ...

—

23

—

6

Total ...

54

38

46

19

Deficit in c:

ropped land 16

27

Indeed, wherever the climate allows, it is good prac-
tice to plough very early in autumn and cultivate well
so as to kill weeds and to give the bacteria a good chance
of producing nitrates for a winter-sown crop. This is
called a bastard fallow. It may even be profitable to
secure an earlier start by sacrificing the aftermath of

^ Journal Board of Agric. xx. 45.

90

The Control of the Soil

[PT. II

the seeds ley. On heavy land it is sometimes found
worth whUe to spend a whole season over the fallow,
sacrificing rent, rates and capital charges, so as to allow
ample opportunity for obtaining these various effects of
spring and summer cultivation.

Fig. 24. Effect of fallowing on nitrate content of soil. The vertical lines
show the amount of water percolating through the soil.

Subsoiling and trenching. The object of these opera-
tions is to increase the root range of the plants.

In ordinary circumstances plants do not have a great
deal of root room : the surface layer, which alone is well
suited to their requirements, is only about 5 or 6 inches
deep — not always as much, indeed — and it is usually
underlain by a subsoil which is not particularly suited
to the plant and from which its roots cannot draw much
nourishment. Any process that makes the subsoil a
better habitat for the roots increases the extent of the
root range and therefore enables the plant to make
better growth. The obvious method of improvement is
to make the subsoil more closely resemble the surface

CH. v] Improvement of Subsoil 91

soil, and in designing the necessary cultural operations
it is necessary to bear in mind the distinctions already
set out (Chapter II) between the surface and the subsoil,
viz., the presence in the subsoil of less food, less organic
matter and less air than in the surface soil, and the
presence of more clay, which is likely to be in the
undesirable sticky state.

The improvement of the subsoil is not commonly
attempted in farm practice excepting only on arable
soils where a plough-sole or a pan occurs near the sur-
face; recourse is then had to subsoiling, and often with
considerable success. The operation is not necessary
oftener than once in four or five years, and it can well
be done as part of the preparation for the root crop.

At Rothamsted subsoiling increased the yield of the
potato crop by about half a ton per acre, but no effect was
visible on the subsequent crops . Striking effects have been
produced in Essex. In Southern Illinois it did not benefit
the cereal crops : if anythingtherewasaslightdepression^.

In fruit growing districts attempts have recently been
made to break the hard layer by means of explosives:
the method is said to be effective in South Africa, but
it was unsuccessful in Scotland.

In market gardening and horticulture it is common
to trench the land with the object of making the subsoil
more like the surface soil. Sixty years ago it was thought
that the subsoil was reaUy the virgin soil, rich in stores
of food that only needed liberating by the action of
frost. Sixty years of experiment have shown that this
is not correct; the subsoil is really very poor in plant
nutrients, and nothing whatever is gained by bringing
it to the surface. Considered as a manure it is des-

1 Rothamsted Ept. 1915-17, p. 68. Illinois Expt. Station Bull. 181, 1915.

92 The Control of the Soil [pt. il

picably poor. This is the general rule ; exceptions arise
when the subsoil contains much chalk or marl, and the
surface soil does not ; or when the subsoil is clay, and the
surface soil is too light a sand. With these exceptions
the subsoil is much poorer than the surface soil, and
therefore to make it equal the gardener must add manure
to it.

To get the subsoil into the same mechanical condition
as the surface soil without bringing it up to the top is
not easy because frost does not penetrate readily. Some-
thing can be done, however, by adding lime, limestone,
chalk, or basic slag, to the subsoil at the time of trench-
ing.

The roots of the plants have a wonderful facihty for
boring their way into the subsoil, and very stout roots
can often be found well below the surface depth. It is
not clear, however, that the loosening of the soil is par-
ticularly helpful to these plants, indeed a soil which is
simply loosened and then left soon settles back to its
natural condition.

Three methods of trenching have been used :

1. The top spit is kept on the top, and manure is
buried in with the subsoil.

2. The digging is done in the same way but no
manure is added, the subsoil being simply loosened.

3. The subsoil is put on the top and the surface soil
below.

These three methods have given rise to much dis-
cussion but there are times when at least two of them
are sound.

The first is practically always beneficial, though it is
not always a commercial success.

Experiments at the Woburn Fruit Farm and at

CH. v] Trenching 93

E-othamsted have shown that the second method (the
loosening of the subsoil without additional manure) has
very little effect either on the water content, the amount
of plant food or the growth of fruit trees. There is no
evidence that this operation is worth doing ; the gardener
who takes the trouble to trench should certainly not
miss the excellent opportunity it affords for putting the
very necessary manure into the lower spit.

There are, however, cases where the third method (the
inversion of the surface soil and bringing up of the sub-
soil) has worked very well, particularly on sandy soils
where the difference between the surface and the sub-
soil is less than on the loams and clays. The subsoil is
not particularly unsuited for the growth of plants, and
when brought to the surface it only requires proper
manuring to enable plants to make a satisfactory start.
Then when the roots grow down to the second spit they
come to the old surface soil and develop well: thus in
the end they range over two spits whereas on untrenched
land they cover one spit only.

We can now make a general summary of the effects of
cultivation; they are:

1. To change the clay — and therefore the soil — from
the sticky state which is bad for plants to the useful
crumbly state.

2. To keep the surface fine so as to reduce the tem-
perature and conserve the water supply on hot fine daj^s.

3. To give the crop a clear field for growth and reduce
competition by weeds: this seems also to enable the
bacteria more rapidl}^ to accumulate nitrates in the soil .

4. In horticultural and market garden practice to
change the subsoil and make it as nearly as possible
like the surface soil.

CHAPTER VI

THE CONTROL OF SOIL FERTILITY

We now turn to the final part of our subject: the
study of the methods by which the fertihty of the soil
may be increased, or, in other words, the soil may be
made more favourable for the growth of plants. The
plant requires from the soil six conditions, viz. :

1. Proper water supply.

2. Proper air supply.

3. Suitable temperature.

4. Nutrient salts.

5. Ample root room.

6. Absence of injurious substances or pests.
These six are all quite distinct: it is no good satisfjdng

five of them if the sixth is not attended to : any single
one left unsatisfied may operate as a limiting factor and
render the soil infertile.

Thus the problem of increasing the fertility of the soil
reduces itself to the discovery, first of the factor or
factors limiting the growth of the crop, and then of the
best methods of overcoming the limiting factors.

Sometimes the fault lies with the soil, sometimes with
its surroundings: in the first case the defects may be
caUed intrinsic, in the second extrinsic. It is necessary
carefull}^ to distinguish between these : there is obviously
no point in spending time and money in doing some-
thing to the soil when the surroundings are unsuitable,
or in elaborately trying to improve the surroundings
when the soil is not worth it.

PT. II, CH. vi] Soil Types 95

The distinction is well illustrated by the following
experiment due to S. T. Parkinson^. A trench was
dug 5 ft. broad, 30 ft. long and 3 ft. deep: the sides
and bottom were lined with loose bricks and stones, and
four partitions were put up. The divisions were then
filled respectively with a good loam, a peat, a gault

LOAM

.^v'

PE/VT

GAULT

3ft.-

Fig. 25. Carrots grown on various types of soil.
(S. T. Parkinson's experiment.)

clay, a poor sand and broken chalk. Carrots were sown
and gave results shown in Fig. 25. The student should
repeat the experiment using typical local soils. The
observed differences depend on the intrinsic properties
of the soil, the extrinsic conditions being the same for all.
The chief intrinsic conditions are that the soil must
be capable of going into a good tilth, that it must con-
tain enough of all the constituents required for the plant
and that it must not be "sour," while the most impor-
tant extrinsic conditions are that it must be sufficiently

1 Journ. Smith Eastern Agric. Coll., Wye, 1910, 258-261.

96 The Control of the Soil [pt. ir

deep, sufficiently suppKed with water during the growing
period of the plant, and exposed to suitable climatic
conditions.

Perhaps the most wddespread soil defect is "sourness "
or "acidity." "Sourness" is a state that cannot easily
be defined although a good cultivator easily recognises
it. It arises through lack of lime and shows itself in a
bad physical state of the soil and in the poor growth and
obvdously unhappy appearance of the vegetation, especi-
ally of clover. It is partly due to deflocculation of the
cla}^ but apparently partly also to the presence of certain
harmful substances formed mider these special con-
ditions. Unfortunately few investigations have been
made in this country on "sourness," but it can be cured
by additions of lime an d proper cultivation . ' ' Acidity ' '
can be recognised readily by litmus paper ; a blue piece
changing to red in contact with an "acid" soil. Until
sufficient lime has been added to correct "sourness" or
"acidity" no scheme of husbandry is likely to be
successful.

As a general rule no soil is satisfactory unless it can
be got into the nice crumbly condition or "tilth" which
the gardener aims at in preparing a seed bed. This re-
quires that the clay should be flocculated, which, as we
have seen, can be done by (1) adding lime or chalk,
(2) adding organic manures, (3) leaving the soil turned
up and exposed to winter frosts, (4) cultivating the soil
only when it is in the right condition and carefully' re-
fraining from touching it when it is too wet. Heavy clay
soils can rarely be got into a good tiltli and hence are
unsuitable for cultivation : light soils easily acquire the
proper tilth: in between come a whole series of soils
which a skilful farmer can manage while an unskilful

CH. vi] Depth of Soil 97

one cannot. But it may be taken as a guiding principle
that if a good tilth cannot be secured either the soil or
the man is at fault and failure is almost certain to
follow.

Again, the soil must be sufficiently deep. Even the
best soil would prove infertile if it were spread out too
thinly on a rock or a gravel bed, or if it were water-
logged to within a few inches of the surface. Most soils
are improved by being deepened, but before deciding
how to proceed a careful examination has to be made on
the spot. The simplest case arises when a thin layer of
rock or conglomerated soU parts the surface soil from
the subsoil below: sometimes such a layer has been
formed in recent times and is known as a pan. So long
as this remains it effectually checks plant growth. When
it is broken up and removed a greater depth of soil is at
once available and plants develop much more readily.
An example of this improvement on a large scale is
furnished by Cox Heath, Maidstone, once a waste, now
a fertile tract^.

Sometimes, however, the rock is solid and then it
obviously cannot be removed. If it lies in regular layers
end on to the surface there is the possibility that some
of the roots may be able to find a way in between, as
happens in the Upper Greensand beds of West Sussex,
but if the layers lie horizontally the chance of success is
much smaller. The case becomes still more difficult
when the soil lies on gravel. The "shrave" of West
Sussex, the commons of Hertfordshire, are formed of
thin soils lying on gravel which could never be managed
satisfactorily in spite of the fact that good farmers have

1 This and other reclamations are dealt with more fully in the author's
Fertility of the Soil, Cambridge University Press.

R. s. 7

98 The Control of the Soil [pt. ii

always been found on the deeper soils round about them.
Modern science has as yet no way to suggest (Figs. 26
and 27).

When the shallowness of the soil is due to water an
obvious remedy consists in lowering the water table by
drainage. Over a large part of England this trouble did
exist, and one of the greatest achievements of the 19th
century was the extensive drainage that was under-
taken. Some of it, of course, was done badly, the drains
being put too deep, and some of it needs doing again
especially where the pipes have become blocked up, but
the improvement was great and lasted for a long time.

Bad drainage is one of the common causes of infer-
tility on heavy soils in this country. It was met in the
old days by lajdng up the land in high ridges several
yards wide (often a rod wide) which were commonly not
quite straight but cur\^ed at each end like a long drawn
out S, the result of a difficulty in turning the ploughs in
the days when a long team of oxen was used. The
scheme had the drawback that the furrows were usually
too wet and too much on the subsoil for a satisfactory
growth, and sometimes the plants failed altogether.
Even a shallow furrow has a bad effect. Moreover the
advent of the binder has necessitated the use of flat
ground and made the old ridges impossible.

Since 1823, when James Smith of Deanston, Perth-
shire, began to draw attention to drainage, large areas
of land have been pipe-drained. The cost is high and
in many cases the result must have involved financial
loss, although the contingent benefits in the countryside
were probably worth it. In the old days there was a
great dispute as to how deep the drains should be laid :
Smith laid shallow drains, and Josiah Parkes, a famous

CH. VlJ

Gravel subsoil

99

ce

6C

a:

S
o

eg

>

S
o

O

c

o
-^

o
O

s

©

o
a,

S
W

CO

100

The Control of the Soil

[PT. II

- ■•■■■\>'

-mi

Chalk subsoil. This land can be cultivated although the
soil is thin. (Harpcndcn.)

Gravel subsoil. This land cannot be cultivated because the soil is too
thin for a gravel subsoil. (No Man's Land. Wheathampstead.)

Fig. 27. InHiionco of the subsoil.

CH. vi] Drainage 101

engineer, who drained Chat Moss and other great areas,
laid deep drains. It is now known that both sides had
a good case : shallow drains are needed when the water
to be removed comes from above — e.g., from excessive
rain or seepage from high land — and deep drains when
the water is thrown up from below. Before deciding on
the depth of the drains, therefore, it is necessary to
ascertain where the water is coming from and how and
where it can best be intercepted.

On clay lands the water usually comes as rain and
therefore shallow drains are best. The pipes are com-
monly 3 in. diameter and are often laid 2| to 3i ft. deep
and at distances of 15 to 30 ft. apart, but an intelligently
thought-out plan is always wanted. The cost is con-
siderable— before the war it was about £7 per acre —
and where it is undesirable to spend so much money a
mole plough often furnishes a cheap and tolerably
efficient substitute especially where there is a reasonable
fall to a ditch. This implement cuts out a 3-4 inch
tunnel 18 in. to 3 ft. below the surface of the soil into
which the water can drain. The tunnel is more per-
manent than might be anticipated, and lasts 15 to 20
years or more, especially if it does not run straight into
the ditch but into the old mains, or, if these cannot be
found and cleared, into new pipe drains discharging into
the ditch^. The method breaks down if large stones are
present; a turf drain might then be tried or even a
surface drain made by casting out a furrow.

Whatever the drainage scheme it is particularly im-
portant that the ditches should be kept clean and the
outfalls of the drains open : the main drainage brook of

^ See paper by D. T. Thring, "Mole-drainage and the renovation of old
pipe drains," Journ. Roy. Agric. Soc, 1914, lxxiv. 76-89.

102 The Control of tlie Soil [ft. ii

the district must also be cleaned regularly. If the land
is not wet enough to need actual pipe drains it may still
require a water furrow to carry away excess of rain, and,
should no natural outlet occur, a sump or a dell may be
made, as is done in parts of Hertfordshire. The great
point is that water must not stand about on the land.

It is not enough that the soil should go into a good
tilth and be of sufficient depth : it must also contain all
the things wanted for the proper growth of the plant.
The soil, in short, must be complete, containing adequate
quantities of sand, silt, clay, calcium carbonate, organic
matter, and the various nutrient salts. Many natural
soils are lacking in some direction or another, but it is
usually possible to make good the defect. The farmer,
however, wants more than this: he wants to make a
profit on the transaction, and therefore a compromise
usually has to be effected between the ideal and the
commercial. Sand can be added if necessary, but 100
tons or more would commonly be required per acre to
make ajiy appreciable difference. This would cost too
much to be practicable in England although it can be
done in countries where labour is very cheap. Clay can
be added at less expense because a dressing goes further
than in the case of sand : the operation becomes a com-
mercial possibility when the clay contains calcium car-
bonate^, so that two desirable constituents are added in
one operation. Illustrations are afforded in the Isle of
Ely, where such clay is obtained from below the surface.
The method consists in laying trenches. 18 yards apart,
and in each digging holes ten to the chain and sufficiently
deep to reach the clay: about a ton is then got from
every hole and spread round about. The cost of the

^ This mixture is called MarL

CH. vi] Cost of Soil Improvements 103

operation before the war was about 505. per acre. A
considerable area of land in the Pays de Waes, between
Antwerp and Ostend, was improved in this way.

Chalk or lime is still more easily added : some 20-40
tons per acre of lump chalk are needed, but much
smaller quantities of ground chalk, limestone or lime
suffice. Organic matter can be added in two ways:
either by adding farmyard manure or other organic
manures, or by green manuring. The nutrient salts can
also be added in the form of various manures.

The question of improving soil in many cases there-
fore reduces itself to one of cost. It has become the
practice in this country to regard the more costly and
permanent methods — such as drainage — as the land-
lord's business, and the cheaper and more transient
methods — such as manuring — as the tenant's business
for which, however, he is compensated if he quits the
holding before a certain interval of time has elapsed.
Now the landlord is not always able or willing to expend
money on costly improvements and the question then
arises : What line is the tenant to take ?

In deciding what to do the farmer must remember
the universal law that the plant must have all its
requirements satisfied and excess of one cannot replace
insufficiency of another. He must therefore get over
each defect as he discovers it. First the obvious defects
must be corrected. Thus if the soil is waterlogged it is
no use putting on manure until a way out has been
found for the water. The farmer may be able to do this
by means of a few trenches or mole-ploughing, but if he
cannot the water will set a limit beyond which his crops
will not grow : it is therefore useless to spend time and
money in trying to make them. Next a good dressing

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106 The Control of the Soil [ft. ii

of weeds was therefore reduced; still later rotations were
gradually introduced; liming and chalking were more
carefully done; drainage was attended to; in the middle
of the 19th century artificial manures were introduced

WHEAT SOILS

] Fine Gravel, larger than 1 mm. 5;.--S^v'^ ^''t, 04 to 01 mm.

Coarse Sand, 1 to 02 mm. W^^^I^M Fine .Silt, 01 to 002 mm.

HIHH Clav, smaller tliAn 002 mm.

Fine Sand, 0-2 to 004 nim.

Fig. 28 o. Mechanical composition of soils well adapted for
certain crop.s.

and tillages were improved ; still more recently improved
varieties and better seed have been available so that
now 40 bushels are readily obtained by good farmers*.

1 Mr Alfred Amos obtained 96 bushels per acre in 1918. See Journ. Bd.
Agric. 1919, xxv. 1161.

CH. VlJ

Uncontrolled Factor,

107

Each improvement has consisted in removing some
factor that was keeping down the yield to a certain
level. But there still remain two sets of factors that

POTATO SOILS

Vm& Gravel, larger
than 1 ram.

Coarse Sand, 1 to 0-2 mm.

Silt, Ot to -01 mm.
Fine Silt, 01 to 002 mm.

Fine Sand, i)-2 to 0-04 mm.

Clay, smaller than -002 mm.

Fig. 28 h. Mechanical composition of soils well adapted for
certain crops.

cannot yet be controlled : the climate and the soil type.
The difficulty is met by growing crops suited to the
coniitions, and this explains why certain crops tend to

108 The Control of the Soil [pt. ii

be grown on certain types of soil. In Fig. 28 are shown
mechanical analyses of the soils on which in the south-
east of England wheat and potatoes are found to do
well.

Clay soils
There are two kinds of clay soils :

1. Those that arise through the presence of 20 per
cent, or more of clay^.

2. Those that owe their properties to the presence of
considerable amounts of fine silt.

They are indistinguishable to the eye and have many
properties in common, but they have this important
difference: the "clay" can be flocculated by lime or by
exposure to frost while the "fine silt" cannot. Hence
the first group can be improved agriculturally by liming
but not the second: indeed so far the "silty" clays have
proved unmanageable.

The first group are the typical clays and are widely
distributed in this country. The fine particles have cer-
tain properties which they impress on the whole soil:
they are sticky when wet but set very hard when dry:
they swell up on moistening and give out a little heat :
they absorb heat and shrink on drying, and thus cause
the large gaping cracks seen in dr}^ weather on clay land.
The fine particles also impede the movement of water so
that the soil is very wet in wet weather but may suffer
from drought in very dry weather.

If the soil is not limed and the drains and ditches
are not well looked after, the clay tends to go into the
deflocculated form (p. 21) and then all the properties
just described are intensified. The soil becomes difficult
to cultivate owing to its persistent wetness: autumn
^ I.e., particles less than 0002 mm. in diameter, see p. 16.

CH. vi] Clay Soils 109

sowing is difficult and sometimes impossible so that
spring crops have to be substituted: the young plants
only get through with difficulty and suffer badly in
spring: a wet summer is bad and a wet harvest worse.
Crops that ought to last a number of years, such as
lucerne, only last two or three. If the land is laid down
to grass the finer deep rooting grasses never get hold,
the plants that survive being the surface rooting Bent
grass {Alopecurus pratensis) which withers during dry
weather and causes the burnt colour so common on poor
clay pastures, the rushes, the coarse file-like Aira cae-
spitosa and other plants specially adapted to wet places
(Fig. 29).

The method of deahng with these soils is simple in
principle but often difficult in practice: it consists of
two parts: (1) arranging a way out for the water by
means of a careful drainage scheme and clean ditches;
(2) flocculating the clay and taking care that it does not
get deflocculated. When this can be done clay soUs be-
come very suited for wheat, beans, and, in the southern
half of England, mangolds, but more especially they
grow good grass so that both meadows and pastures are
common. Considerable trouble arises from the fact that
plant roots do not develop quickly and that crops do
not readily ripen. Now we shall see later that phos-
phates have the special effects of inducing good root
development and of hastening maturity, and we shall
therefore expect that phosphates would prove very
beneficial on clay soils. Experiments all over the
country show that this expectation is well founded:
phosphates have a very considerable effect in improving
the productiveness of clay soils.

The crop most generally suited for clay soil is grass.

110

The Control of the Soil

[PT. II

and therefore the agriculture usually centres round live
stock, dairying, etc. The manurial treatment is simple,
lime and phosphates being the two chief requirements,
and these can be convenientlj'^ supplied in dressings of
basic slag. Where land is laid in for hay, nitrate of soda
or sulphate of ammonia should be supplied in addition.

Fig. 29. Poor clay country. Roads wide but not all made up,
hedges and gates not well kept.

The arable land must receive dung and periodical dress-
ings of chalk or lime in addition to the phosphates. The
treading of the horses tends to make a plough-sole which
has periodically to be broken by means of a subsoiler,
or, where steam cultivation is adopted, by putting a
few extra long tines on the cultivator. But above all,
drains and ditches must be kept clean. Autumn work
must always be pushed well forward to allow as much
winter sowing as possible, winter corn and beans being

CH. vij SUty Clays 111

more successful than spring corn. Latesowingsonl}/ come
to anything if the seed goes in well. Swedes and potatoes
are not easy to grow and fallowing is necessary in order
to keep the land clean and in good tilth; a bastard
fallow may suffice, especially if it can be started early
enough, but an occasional dead fallow lasting over the
whole season is desirable and gives very good results,
especially if the summer is hot and dry and the winter
not too wet. Grass land which is being changed to arable
should be broken up in autumn, using by preference two
ploughs, one to skim off the grass and the other to bury
it. Disk implements may, however, be sent over to cut
up the turf before ploughing.

The second class of clays, the silty clays, are very
truculent to deal with and no reliable method has yet
been evolved. They can be found in the Lower Wealden
beds in the district east of Horsham, on the Boulder
Clay, the Coal Measures, etc. : they occur at Garforth in
the West Riding and in numerous other places; every-
where they have a bad reputation which they thoroughly
deserve. Lime and subsoiling have less effect than might
be expected, and probably the best treatment is to mole
drain them and lay them down to grass : it is not worth
while spending much on them as they do not respond
well to treatment.

Sands

The chief agricultural properties of sandy soils arise
from the fact that they are porous and readily allow the
passage of water. Thus the water never accumulates
and the soils only get waterlogged when they are under-
lain by a basin of clay : usually they suffer from drought
in dry weather. In its passage the water carries with it

112 The Control of the Soil [pt. ii

much of the soluble matter: sometimes indeed so much
that even weeds will not grow but only patches of moss
which decay to a black acid substance entirely unsuited
to most plants : such patches can be seen frequently on
the Bagshot sands in Surrey.

Where there is a fair admixture of silt the movement
of the water is retarded, and on moving aside the top
two or three inches of soil the lower part is found to be
quite moist even in dry weather. In these cases plants
will grow well and a special type of treatment has been
evolved to suit them.

In the first place the movement of the water has to
be still further retarded, and regular additions of organic
matter are therefore necessary. Secondly, lime has to
be added regularly except in certain special cases where
the soil lies at the foot of a long gradual slope and re-
ceives an underground drift of hard water from above.
Lastly, fertilisers have to be added in small but frequent
doses when the crop needs them. When these pre-
cautions are taken sandy soils will grow almost any
crop, but they especially favour the development of
roots and tubers so that they are well adapted to
potatoes, carrots, parsnips and nursery stock; further,
they give good quality barley and useful but not large
wheat crops. They are not suited for grass unless the
water table happens to be only 3 or 4 feet from the
surface in which case they may carry magnificent pas-
ture : some of the very best Romney Marsh pastures are
on sand. Otherwise the grass burns up badly in the
summer time owing to lack of water.

Sandy soils tend very much to form pans, and care
has to be taken to prevent this by occasional use of the
subsoiler.

CH. vi] Sandy Soils 113

The management of sandy soils turns on the method
by which the organic matter is to be added.

(1) If stable manure is available in large quantities
a succession of heavy crops can be obtained, and re-
course is then often had to market gardening: this is
done on the sands near London, around Sandy in Bed-
fordshire, in parts of Essex and elsewhere. Where the
market facilities are not quite so good potatoes can be
grown on a dressing of 12-15 tons of stable manure,
and a mixture of artificials rich in potash; a grain crop,
two "seeds" crops, and another grain crop can then be
grown on the residues and without further manure. The
aftermath of the first seeds crop can be fed ofE with hay,
cake, etc., while the aftermath of the second is ploughed
in. The adoption of this method in Hertfordshire has
enabled farmers to prosper on land which previously
ruined its occupiers.

(2) The organic manure may be supplied through the
agency of live stock. Sheep may be kept throughout the
winter and folded on to green crops such as rape, kale,
winter barley, swedes, vetches, etc.; in addition they
receive purchased feeding stuffs. The droppings from
the animals fertilise the soil and return to it a consider-
able part of the substance of the crops and feeding stuffs
supplied. Moreover the trampling of the animals has
the further advantage of consolidating the land. The
sheep have to be fattened and sold before summer or
else removed to cooler pastures on higher ground, on
chalk, etc. The same principles hold, with suitable modi-
fication, where bullocks are kept: home grown fodder is
supplemented by purchasedf ceding stuffs, the bullocks are
fattened and sold and the manure, whichcontains much of
the straw grown on the farm, is carted out on to the land.

R. s. 8

114 The Control of the Sod [pt. ii

In both cases the organic matter added to the soil
comes largely from the air, being built up by the crop
under the influence of sunshine : in passing through the
animal some is used up but much is excreted.

(3) A third method of adding organic matter to the
soil consists in ploughing in a leafy crop : this is known
as green manuring and may be adopted wherever live
stock are not available. It is a very old method, but has
come into considerable prominence since Schultz in 1880
enormously improved his estate of barren sand at Lupitz
at very small cost by growing lupins fertihsed with
potash, phosphates and lime and then ploughing them
in. The lupins, being leguminous plants, fixed nitrogen
from the air and thus increased the stock of nitrogenous
organic matter in the soil: indeed they acted like a
dressing of farmyard manure. Various modifications
have come into use: in this country mustard is some-
times used for the purpose and is found on the sandy
soil at Woburn to give better results than vetches,
although it is a non-leguminous crop: on the heavier
soil at Rothamsted, however, it gives poorer results:

Yield of wheat, bushels per acre

At Woburni

At Rothamsted^

After vetches

151

36-2.5

„ crimson clover

—

28-5

„ mustard

25-1

25-8

„ rape

20-4

22-6

No green crop

10-1

17-5

Green manuring has not been extensively adopted in
this country because farmers prefer to feed their crops
to stock and so get fat animals as well as manure. But

1 J. A. Voelcker's experiments, Four years: 1906, 1908, 1910, 1912.

2 Three years: 1907, 1910, 1912

CH. vi] Manuring of Sandp Soils 115

it seems probable that more use might with advantage
be made of the system and that the organic manure
added to the soil should not be limited by the number
of animals the farmer may find it convenient to keep.

Whatever the system of agriculture, it is desirable to
crop as frequently as possible because sandy soils lose
a great deal of their fertilising constituents if left bare
and exposed to the rain. The cultivations must also be
thorough to keep down weeds: no soils are so prone to
be smothered with weeds as are sands.

The manuring has to be decided by the crop : reference
has already been made to the paramount importance of
organic matter and of lime : potash is wanted for many
cropS; especially potatoes., while phosphates are usually
needed to prevent rankness in the grain crops taken
after green crops have been fed off and also to secure the
maximum feeding value of the green crops themselves.

Soluble manures must only be added in small quan-
tities at a time because of the ease with which they are
washed out. Sandy soils have less capacity than clays
for absorbing soluble substances: this can be demon-
strated by the following experiment. Dissolve 0-3 gram
of superphosphate, dilute to 500 c.c. and divide into two
lots of 250 c.c. To one add 50 grams of a light sandy-
soil, and to the other 50 grams of a heavy clay soil,
shake both solutions well for 3 minutes, allow to settle
-for 3 minutes, shake, and settle again. After 15 minutes
filter. To 50 c.c. of each filtrate add 10 c.c. of ammonium
molybdate solution (p. 233). Much more precipitate is
obtained from the sand than from the clay.

A similar experiment with a weak solution of am-
monium sulphate (2-5 grams per litre) in place of super-
phosphate shows that clay also absorbs ammonia more

8—2

116 The Control of the Soil [pt. ii

completely than sand. In this case 25 c.c. of the filtrates
are distiLled with caustic soda and the ammonia in the
distillates determined by titration.

A third experiment with burnt sugar solution proves
that soluble organic matter, like ammonia and phos-
phates, is absorbed to a greater extent by clay than
by sand.

Sandy soils and light soils generally are very attractive
because they are more under control than most others.
No matter how wet the season they can be worked. An
intelligent man may get two crops in the year from part
of the land: after early potatoes, for example, he may
take cabbage, sprouts, or sprouting broccoU. Straw-
berries can be successfully grown and many other
valuable crops. No rigid rotation can be adopted: there
must always be a certain amount of cross -cropping. Few
soils, however, are so entirely dependent on the skill and
intelligence of the farmer. Some of the best farms in
England are to be found on the sands : they are managed
on sound Unes, well manured, kept free from weeds, and
made to yield heavy crops: labour-saving devices are
introduced and the skilled hands are well paid. On the
other hand bad management speedily ruins the land and
the farmer: docks, bindweed, sorrel, com marigold,
spurry, and a host of other weeds soon come in and
before long the land is useless.

Loams

Loams come in between sands and clays and can only
be defined as soils which are not as heavy as clays and
not as Ught as sands. Usually they contain not more
than 10 to 15 per cent, of clay and not more than 20 per

CH. vi] Loams 117

cent, of coarse sand ; they are chiefly made up of inter-
mediate material. All shades of loams exist, from the
light loams which some would call sands, to the heavy
loams which can also be called clays.

Loams are by far the most fertile soils in the country ;
instances are to be found in the brick earths of East
Kent and near Chichester, the alluvials of some of the
famous vales and of the Evesham district, the famous
Carse of Gowrie (locally called a clay) and many others.
Practically any crops will grow — climate permitting, of
course — and the cultivator may adopt any scheme of
management he finds most profitable.

Usually speaking bullocks or dairy cows play the
central part on the heavy loams and sheep on the light
loams, the animals in both cases being required to act
as manure-making machines, and also to convert the
less portable products such as straw, roots, etc., into
portable and saleable meat. As an illustration of heavy
land arable farming : in parts of Oxfordshire the land is
farmed roughly on a four course shift of clover, wheat,
mangolds (with some swedes), oats (and some barley) —
swedes and barley being less suited than mangolds and
oats for heavy land are not so widely grown. In the
second period beans are taken in place of clover (which
becomes "sick" if attempted too often) and are well
dunged as they are a profitable crop. There is a good
deal of grass. Dairy cattle are kept by some : others buy
yearling stores at a low price and keep them till they are
worth considerably more, then sell them out to be
fattened elsewhere. On the light land the traditional
rotation is clover, wheat, swedes and barley : the swedes
and the aftermath of clover are fed off by sheep which
also receive cake, etc., the wheat and barley can be sold,

118 The Control oftlie Soil [pt, ii

but there are many variants and many farmers indeed
have no fixed rotation but grow those crops that promise
to be profitable at the time. Among the crops introduced
in the rotation in the eastern counties are peas, sainfoin
and lucerne : elsewhere the number of crops varies and
there is taken one green or root crop to two grain crops.
It is not our business to discuss the rotations in detail
but only to consider their effects on the soil. The root
crop may be either swedes, kolil-rabi, cole, mangolds,
turnips or potatoes as convenience requires : in any case
its effect on the soil is to afford an opportunity for ex-
terminating weeds, and the frequency with which it is
taken is determined in part by this consideration.

Now light soils are very prone to weeds, in particular
to charlock {Brassica sinajns). Heavy soils suffer less,
but still are liable to docks, thistles, etc. Charlock can
be kept down by spraying^, the others cannot. Some-
times the land will keep clean for four and sometimes
for five years : in that case two corn crops can be taken
in succession and a winter oat crop inserted between the
wheat and the roots: or the clover may be replaced by
a mixture of clovers and grasses which can be left for a
period of years. Again, the root crop may be eaten in
the field by sheep wherever the soil is not too wet, and
the soil then receives not only the fertilising constituents
derived from the crop but also those derived from the
added feeding stuffs. This furnishes an extremely useful
method of fertilising the soil for the next crop : it reduces
the losses of manure to a minimum (see p. 170), it saves
cartage of manure, and it enables rapidly grown catch
crops to furnish their quota to the organic matter of the

^ A 3 per cent, solution of copper sulphate sprayed in early spring at the
rate of 50 gallons per acre

CH.VI] The Root Crop 119

soil. But the method is not feasible in heavy soils be-
cause sheep "poach" the land too badly and ruin the
tilth; here therefore the roots have to be drawn off,
farmyard manure made and carried out on to the land.

A third effect of the root crop is that it affords the
best means we have now for fallowing the land. In old
days bare fallows were adopted: now they are uneco-
nomical. But it appears that bare fallows do have a
remarkable effect on the crop especially in enabling a
more vigorous start to be made. Now the root crop is
usually taken after a corn crop, so that the land is well
cultivated but uncropped from November or December
to the time of sowing; cultivation continues, and the
land is almost uncropped till June, when the root crop
begins to grow; indeed cultivation sometimes goes on
longer. The grain crops, on the other hand, follow con-
tinuously: the barley is seeded with clover so that the
land is not even ploughed between these two crops : the
clover is ploughed in just before the wheat is sown, and
if winter oats follow, this crop in turn is sown just after
the wheat is harvested. Only when the root crop comes
round is there much opportunity for cultivating the soil
well and giving it the benefits of the fallow effect. There
are of course exceptions : in forward districts the harvest
may come so early that steam tackle can at once be put
on to the land and a bastard fallow given before the next
corn crop : it is then not necessary to give a rest between
the corn and the roots but a series of catch crops can be
taken.

The root crop also gives a good opportunity for deep
ploughing or subsoiling.

So important is the root crop that special care is taken
to secure a good seed bed and to supply appropriate

120 The Control of the Soil [pt. ii

manures. Experiments on the best way of preparing the
bed are badly needed : there is great diversity of opinion
among good practical men on the subject. Numerous
manurial experiments have been made, however, and
have demonstrated the need of adding lime wherever
finger and toe {Plasmodiophora brassica) is common, of
supplying nitrogen compounds, phosphates, and on
light soils potash as well.

The efifect of the clover or seeds mixture on the soil is
that it adds nitrogenous organic matter to the soil (p. 45).
Experiments have shown that crop residues of this sort
not only increase the soil fertility by the additional
nitrogen thus introduced, but they are particularly
valuable in reducing the harmful effects of bad weather
on the soil, and steadying the fluctuations of soil pro-
ductiveness produced by bad weather. This is well
illustrated by a comparison of the wheat crop taken
after clover (supplemented by artificial fertilisers) on
the Agdell Field at Rothamsted, with that on the
Broadbalk Field where no green crop is ever ploughed
in but where a liberal dressing of artificials is given. On
an average the Agdell plot gives a yield of 34| bushels
against 29| on Broadbalk, and it is a much steadier crop.
It has only twice fallen below 25 bushels, once in 1867
and again in that notorious year of disaster 1879, when
it fell as far down as 13| bushels. But the Broadbalk
plot which has never been green manured fluctuates to a
much greater extent; the yield has frequently dropped
below 25 bushels (Table TV).

American experiments have led to substantially the
same results^.

^ See Minnesota Bull. No. 125, 1912 : Ohio Circular, No. 131 : and experi-
ments in Iowa and Illinois quoted in Hosier and Gustafson, Soil Physics.

CH. vi] The Lighter Loanis 121

Table IV. Steadying effect of

crop residues on yield

of wheat

After clover

ploughed in;

complete

artificials

After previous

wheat crop;

complete

artificials

Average of all

35

30 bushels

Highest yield, 1863

46

56

Low yields, 1871

25

13|

1875

31

11

1879

13

5

1903

2S

24

It is a common practice in the North of England and
Scotland to leave the seeds mixture for 3, 4 or more
years.

The clover crop is so necessary that great pains must
be taken to secure it. Unfortunately it cannot be grown
very frequently on the same land in England as it suffers
from diseases and pests called generally "clover-sick-
ness" for which no practicable remedy is yet known^.
If this trouble arises a dressing of lime should be given :
if this fails a dressing of sulphate of potash (2 cwt. per
acre) may be tried and if this still fails another legu-
minous crop ought to be grown.

The lighter loams tend to be used for special crops
Hke fruit, market garden and nursery produce, malting
barley, etc., and their management then requires very
great skill and intelligence. Some have always been used
for these purposes, such as the Thanet Beds of East
Kent, but many of them, like the sands, were formerly
held in but little repute, and have only during the past
30 or 40 years come into favour. The New Red Sand-
stone of Somerset , affords instances of light loams not

1 See Arthur Amos, Journal of the Farmers' Club, May, 1916.

122 The Control of the Soil [pt. ii

very suited for ordinary agricultural purposes, but well
adapted to fruit, market gardening, etc., wliile the light
loams round Porlock are famous as the source from
which many prize samples of barley have come to the
Brewers' Exhibition.

Chalk soils

Chalk soils are usually very light loams but they re-
quire special attention because of their great economic
importance. Like all light soils they are hable to drought
but they possess the unfortunate property- of drjdng to
hard steely fragments unless they are worked to a good
tilth at the proper time : they therefore require special
care in cultivation. Organic matter is very necessary
for them, and sheep therefore play a large part in chalk
districts. Further, during frosty weather they become
so puffed up and lightened that the young crops are
sometimes almost forced out of the ground: rolling is
therefore necessary in the spring not only on the grass
but also on the arable land.

Leguminous crops are especially valuable on the chalk
bj'- reason of the organic matter they introduce ; among
the most useful are sainfoin and lucerne, the latter
especially in the drier regions or where there is no sub-
soil water.

Chalk soils are highlj^ favourable to plant and animal
life, but this has its disadvantages: they carry a very
varied flora and care is needed to keep down weeds,
especially charlock. Swedes and the brassica tribe
generally are liable to attack by the turnip fly {Phijllo-
treta iiemorum), and all crops to damage by wireworm.

The central feature of the manuring is the folding of
sheep: superphosphate is needed for the roots, and

CH. vi] Peat and Fen Soils 123

potash manures for the clover or seeds ley. On the grass
land basic slag often effects remarkable improvements
especially in the wet districts or where the top inch or
so of soil has lost its calcium carbonate.

Peat -soils

Three kinds of peat soils occur in this country :

1 . The fen soils of Huntingdonshire, Cambridgeshire
and Norfolk, forming a large area of low lying land that
would be flooded by the rivers but for the elaborate
system of embankments and pumps. These soils pro-
duce heavy crops of potatoes, oats and wheat : they also
grow mustard for seed, buckwheat, and if need be,
celery. The fen that lies over Kimmeridge clay is greatly
benefited by dressings of the clay brought up from below
the surface. The fen remote from the clay is not so
readily improved : com crops suffer particularly in that
they do not produce much grain. In cultivating fen
soils the great need is to keep down weeds and leave the
land sufficiently compact. Oxidation and erosion are
rapidly taking place, and even within living memory
have caused much shrinkage of the fen.

Usually speaking lime is not required for crop pro-
duction. The great need is for superphosphate, of which
extraordinarily large dressings are sometimes given with
profitable results. These abnormal features probably
arise from the fact that the waters feeding the Fen
streams all come from chalk land, and therefore bring
with them large amounts of dissolved chalk.

No Livestock is kept and no farmyard manure is
needed.

2. Loiv lying peat lands. These occur to a consider-
able extent in the western half of England, in Wales and

124 The Control oftlie Soil [pt. ii

in Ireland. Unlike the fen soils they are sufficiently acid
to need lime or chalk. Two general methods of treatment
have been adopted : the peat is dug out and sold as fuel,
then the underlying ground is cultivated; or the peat is
ploughed and cultivated direct. Drainage is a first
essential. Oats, potatoes, buckwheat and many grasses
will grow well, but lime is needed for almost any crop,
and in many cases potash as well.

The cultivation of this tj'pe of land has been reduced
to a fine art in Holland and Belgium, and companies
have been formed for the purpose of reclaiming areas
previously waste. The general method of procedure is to
drain, then plough deeply, to add sand or lime, leave for
a time to the action of the weather, then plough again,
add lime and the proper artificials, and finally harrow
down, when a good seed bed can be obtained. Where it
is proposed to keep animals (as will usually be done) it is
necessary to grow clover, and for this purpose f armj'^ard
manure is applied, preferably made into a compost with
good soil. It is probable that the benefit is due among
other things to the introduction of the clover organism
which is not normally present in peat soils. The success
of the reclamation demands a proper rotation and a
suitable scheme of manuring.

3. High lying peat land. In the northern counties
there are considerable areas of moorland at high alti-
tudes which, however, seem wholly unsuited to cultiva-
tion. The rainfall is high and the winters are inclement:
drainage would be a serious difficulty. The few experi-
ments that have been made are not particularly en-
couraging and new methods of treatment would need
to be evolved to give any promise of success.

CH. vi] General Considerations 125

Summary

In order to get the best out of the land an inspection
must be made to see what are likely *to be its chief de-
fects, in other words, what will constitute the limiting
factors. There may, be insufficient water or excess of
water, insufficient depth of soil, insufficient of any of
the proper constituents: [a) of clay, when the soil will
not hold together but will blow about; (6) of calcium
carbonate, when the tilth will be poor and the soil sour
as shown by the presence of sorrel, the failure of clover,
and by poor growth generally; (c) of organic matter,
when the tilth will be unsatisfactory; {d) of various
nutrient substances.

The defect may arise from the fault of the soil itself
or of its situation.

Any defect of this kind will set a limit beyond which
the crop cannot be increased. To remove the defect may
be the landlord's business rather than the tenant's, but
it is useless to try and force the crop beyond the limit
thus set. Once the defect is removed, however, better
crops can be obtained.

The central features of management in cropping land
up to its full capacity are :

Crops and varieties are selected that are specially
suited to the conditions. Some crops such as buck-
wheat, rye and flax will tolerate bad conditions ; others
will not.

Sufficient lime or chalk is added. The land is periodic-
ally subsoiled or ploughed deeply. Every effort is made
to keep up the supply of nitrogenous organic matter in
the soil: leguminous crops are grown: "seeds" are left
for two or three years and sometimes crops are grown

126 Tlie Control of the Soil [pt. ii, ch. vi

simply to be ploughed in. The supply of plant nutrients
is kept up by the addition of appropriate artificial
manures and by suppljdng imported foods to sheep on
the land and to cattle in the yards, when much of the
fertiUsing constituents are excreted and thus get on to
the land.

Wherever the soil is not too wet or sticky the rotation
is so arranged as always to provide a crop that sheep can
eat. Part of the land is kept in permanent pasture and
thus becomes richer in nitrogenous organic matter. The
necessary mineral food is added in the form of phos-
phates and potassium salts.

PART III

FERTILISERS
CHAPTER VII

THE NITROGENOUS FERTILISERS

In attempting to satisfy the various fertility require-
ments discussed in the previous chapter it becomes
necessary to increase the amount of plant nutrients in
the soU and to this end various substances are added
which are known as fertilisers and manures. The dis-
tinction between the two terms is not very sharp, but
generally a fertiliser is a concentrated substance im-
ported on to the farm from a foreign country or a
factory, and therefore is frequently called an artificial
fertiliser, while a manure is a more bulky material either
produced on the farm or closely related to farm pro-
ducts.

The substances thus added to the soil are compounds
of nitrogen, phosphorus and potassium: also organic
matter and lime or chalk. In order to study their effect
on the soil a series of pot experiments should be started :
10 inch flower pots are sufficiently good for ordinary
purposes but for finer work Doulton's glazed pots must
be used (Fig. 1). The soU has to be carefully mixed to
ensure uniformity and if it is heavy 10 to 20 per cent,
of sand must be added. The series should contain pots

128 Fertilisers [pt. hi

treated as follows: (1) unmanured; (2) and (3) 0-01 and
0-05 per cent, respectively of nitrate of soda; (4) 0-1 per
cent, superphosphate; (5) 0-1 per cent, sulphate of
potash; and three or four containing combinations of
these quantities; other pots should be supplied with
sulphate of ammonia in place of nitrate of soda, and
bone meal and basic slag in place of superphosphate.
If a glass house is available tomatoes are a good crop
for experiment; or at colder seasons mustard. For out-
door work rye, wheat or mustard do well.

Two types of nitrogenous fertilisers are in common
use; nitrates which are ready and ammonium salts
which are almost ready for immediate use by the plant
and are therefore quick acting, and certain organic com-
pounds which have to undergo decomposition in the
soU. The first only are dealt with in this chapter.

Nitrates

Three nitrates are now available as fertilisers: the
nitrates of soda, of potash and of lime, and experiments
are being made with a fourth, nitrate of ammonia, but
of these the commonest is nitrate of soda (NaNOg). This
substance occurs in the rainless regions of Tarapaca and
Antofagasta in the north of Chile, where it forms de-
posits near the surface of the soil. The deposits occur
in detached areas stretching over a wide range and in
spite of the large annual consumption — nearly 2,500,000
tons before the war — there still seems a vast supply for
the future. It is not known how the deposits originated :
there is little doubt that they were once under water,
but there is nothing to sliow how so much nitrate came
to accumulate in one district: only traces occur in

CH. viij Nitrate of Soda 129

ordinary sea-water. The crude nitrate is excavated by
a process of trenching, it is then crushed, purified by
recrystallisation and put up in bags for the market.

The commercia] product is not quite pure, but it is
guaranteed to contain 95 per cent, of nitrate of soda and
often contains even more.

Nitrate of soda is very quick acting as a fertiliser and
can be taken up immediately by the plant. It finds
application in two cases: (1) in case of emergency, when
young plants are suffering through the attack of a pest,
or in cold wet weather; (2) in ordinary practice as a top
dressing for the crop. It causes increases of practically
aU crops in England and the dressing applied varies
from 1 cwt. per acre, suitable for wheat in spring or
grass laid in for hay, to 10 cwt. per acre used on the
valuable early cabbage and broccoli crops in Cornwall.
In other countries, however, good returns are not always
obtained: in parts of Australia and New Zealand phos-
phates are the limiting factor : in Western Canada water
appears to be; in none of these cases do nitrates give
the same high returns as in this country.

Besides causing increased growth nitrate of soda pro-
duces certain qualitative effects on the crop. It imparts
darker green colour and greater size to the leaf : in the
case of straw crops it may so enlarge the leaf and the
head that the straw is unable to carry the weight in wet
weather, and the crop becomes laid. Applied in excess
it tends to thin the cell walls, making them more readily
penetrated by fungoid pests, and it also appears to affect
the composition of the sap in some way so that the fungi
develop more readily than usual.

In addition to these effects on the plant another effect
is produced on the soil. The nitrate of soda is not taken
B. s. 9

130 Fertilisers [pt. hi

up. or at any rate not retained, as a whole, by the plant
but a decomposition takes place, the nitrate part being
kept by the plant while some of the soda remains in the
soil as sodium bicarbonate. This reacts on some of the
potassium compounds in the soil, Uberating a certain
amount of potash which then becomes available for the
plant; this has been demonstrated by actual field experi-
ments at Rothamsted, and is also illustrated by the
experiment on p. 135. But the bicarbonate also acts on
the clay, converting it into the sticky defioeculated
state, and on a heavy soil this action becomes rather
serious, causing much damage to the tilth. A suitable
remedy is found in dressings of lime or addition of sul-
phate of ammonia to the nitrate. The student who is
interested in the history of the subject will find that, in
the old papers, nitrate of soda is sometimes called a
"scourge," and some of the older farmers still retain a
dislike to it. This idea probably arose partly from its
harmful effect on the texture of a heavy soil and partly
from its effect on hay land. It encourages a very good
growth of top grasses and may be used A\dth great ad-
vantage whenever hay is sold. But the heavy crop
naturally draws on the soil phosphates, and unless those
are replenished at the same time the soil becomes im-
poverished and the crop ultimately falls off in quantity,
while weeds and poor grasses appear and bring down the
quality. Grass land should never as a regular course be
fertilised with nitrate only, but should periodically re-
ceive the other necessary fertilisers.

Nitrate of soda readily washes out of the soil and
must therefore not be applied until it is needed. It
is best put on as a top dressing when the plant is up :
when this course is adopted the loss in a wet season is

CH. vii] Potassium and Calcium Nitrates 131

reduced to a minimum : there is the further advantage
that the nitrate of soda does not come in contact with
the superphosphate (which is drilled with or before the
seed) : unless thej'^ are very dry these two fertilisers do
not mix well although if put on at once the mixture can
be used where labour is scarce. Heavy dressings such as
are used in market gardens should be applied in two or
three lots and not all at once.

Perchlorates are occasionally present in nitrates and are
very dangerous, as little as 1 lb. per acre causing injury.

The ordinary nitrate of soda of commerce contains
15-5 per cent, nitrogen and its pre-war price was about
£11 per ton f.o.r.^; each per cent, or "unit^" of nitrogen
therefore cost 14s. ^d., and each pound of nitrogen cost
8d. Since the war it has been practically unobtainable
by farmers.

Nitrate of fotash (KNO^)

This substance is dearer than a mixture of nitrate of
soda and sulphate of potash supplying the same ingre-
dients, and therefore it is not used in this country. But
being much less bulky than the mixture it finds con-
siderable application in countries where valuable crops
are raised and freights are high: thus it is used in the
Canary Islands and elsewhere under similar conditions.

Commercial nitrate of potash contains nearly 14 per
cent, of nitrogen.

Nitrate of lime

Of recent years a considerable quantity of nitrate of
lime has been manufactured and prior to the war was
put on the market for use as a fertiliser. The industry

^ F.o.r. =free on rail. Prices delivered to the buyers station may
average about 10s. per ton extra.
- Sec p. 206.

»— 2

13'2 Fertilisers [pt. in

was started by Sir William Crookes in 1 898, and is carried
on at Notodden in Norway and at Niagara where abun-
dance of cheap water-power occurs, and the process con-
sists in burning air in an extremely hot flame — probably
3000°-3500° C. — by means of a powerful electric arc in
a small chamber : the products are then made to react
with lime.

In ordinary circumstances nitrogen is not combustible
and the mixture of nitrogen and oxygen in the air is not
inflammable, but at this very high temperature the
nitrogen bums and unites with the oxygen to form
oxides, chiefly nitric oxide. The gases are cooled, and
mixed with air, when a higher oxide, nitrogen peroxide,
is formed ; they are then drawn with fans through towers
packed with broken quartz down which water trickles,
and become converted into a dilute mixture of nitrous
and nitric acids and finally into nitric acid. This is then
neutralised with limestone and the solution on evapora-
tion yields calcium nitrate i.

The first samples to be placed on the market were not
easy to use as they so readily absorbed moisture and
became converted into a sticky pasty mass, but this
difficulty was overcome prior to the war by making a
basic nitrate; the samples then obtainable contained
13 per cent, of nitrogen.

As a fertiliser calcium nitrate closely resembles sodium
nitrate, but it appears to be free from the disadvantage of
making heavy soils sticky. Further experience is needed
before any very definite statements can be made, but so
far as present knowledge goes nitrate of lime is a very
promising addition to the list of nitrogenous manures.

' For details of the process of manufacture see paper by Eyde, Journal
of the Royal Society of Arts, 1909, vol. Lvii. p. .568.

CH. vii] Sulphate of Ammonia 133

It was not obtainable by farmers during the war. b^lt
it is likely to be produced in great quantities in the near
future as considerable improvements in the process of
manufacture have taken place.

Sulphate of ammonia

This substance is manufactured from coal. The
potential supply is enormous: a ton of coal contains
on an average some 25 lbs. of nitrogen, equivalent to
just over 1 cwt. of sulphate of ammonia. Unfortunately
most of our coal is burnt under such conditions that the
nitrogen is lost, but in certain industries, especially in
the manufacture of coal gas, of producer gas, in coking
ovens, etc., special recovery methods are used and
sulphate of ammonia is obtained as a by-product^. The
world's output in 1913 was well over one and a quarter
million tons, this being nearly three times the quantity
produced in 1903. The process is not costly and it seems
capable of considerable extension . By far the largest pro-
spective supply, however, is that obtainable direct from
the air by the Haber process, in which gaseous nitrogen
and hydrogen are brought together under pressure and
at a certain not very high temperature in presence of a
catalyst. They then unite to form ammonia which can
be passed into sulphuric acid and converted into
ammonium sulphate, or else oxidised by the Ostwald
process to nitric acid, which then can be converted into
sodium nitrate, calcium nitrate or ammonium nitrate.
These processes have developed enormously during the

^ For details of the recovery methods see art. "Ammonia" in Thorpe's
Dictionary of Applied Chemistry. In gasworks one ton of coal yields on
the average 22'7 lbs. sulphate of ammonia: in the Mond producer gas
plant it yields 75 to 85 lbs.

134 Fertilisers [pt. in

war, and the products are likely to be obtainable in
immense quantities in the future^

In its general action sulphate of ammonia differs but
little from nitrate of soda, and the choice between them
is mainh' one of price and convenience. It possesses,
however, certain characteristic features which some-
times assumes considerable importance.

When applied to the soil it reacts with the calcium
carbonate, giving rise to calcium sulphate and am-
monium carbonate. The calcium sulphate washes out
in the drainage-water, but the ammonium carbonate
does not, bemg absorbed by some of the reactive con-
stituents of the soil (p, 21). The ammonium carbonate
becomes nitrified by bacterial action, and presumably
is changed to calcium nitrate through interaction with
more calcium carbonate. Thus the complete change re-
quires that one molecule of ammonium sulphate should
react with two molecules of calcium carbonate, thus :

(NH4)2S04 4- 2CaC03 + 8O2

- CaSO^ + Ca(N03)2 + 4H2O + 2CO2.

On this basis a dressing of 132 lbs. of ammonium
sulphate {i.e., one molecular weight) involves the re-
moval from the soil of 200 lbs. of calcium carbonate.
Now actual analyses at Rothamsted show that only one
half of this quantity, i.e., only 100 lbs., is removed,
and further experiment has shown that the calcium
nitrate is not whoUy retained by the plant but the cal-
cium is left in the soil and re-converted into carbonate^.

There still remains, however, a loss of 100 lbs. of cal-
cium carbonate for each 132 lbs. of ammonium sulphate
applied, and on soils deficient in lime this becomes very

^ Hall and Miller, Proc. Roy. Soc, 1905, 77 b, I 32.

CH. vii] Acid Effects 135

serious for two reasons: the lime is greatly needed for
other purposes ; and in its absence ammonium sulphate
leaves an acid residue in the soil, the ammonium portion
being more completely taken by plants than the rest.
Now most agricultural plants will not tolerate this
acidity, and in extreme cases completely refuse to grow.
This remarkable action was first observed by Dr Wheeler
at the Rhode Island Experiment Station in 1890^ and
was investigated in an important series of experiments
which showed that the trouble could be completely re-
medied by dressings of lime. A few years later the same
phenomenon appeared at the Woburn Experimental
Farm and has been fully described by Dr Voelcker^;
there also lime was found to be the proper remedy.

Thus sulphate of ammonia tends to make the soil
acid, and therefore physiologically unsuited for plants,
while, as already pointed out, nitrate of soda tends to
make it alkaline and therefore physically unsuited to
them. A mixture of the two fertilisers produces no such
effects, as each neutralises the other.

Sulphate of ammonia, unlike nitrate of soda, is com-
pletely absorbed by the soil and shows no tendency to
wash out. This can be demonstrated by packing 50grams
of soil (preferably a loam) on to a funnel, moistening with
water and then pouring on 100 c.c. of 1 per cent, ammo-
nium sulphate solution. Test the filtrate for calcium, for
sulphate, and for ammonia. The two former occur in
quantity, but the ammonia is reduced in amount. Now
repeat the experiment with a fresh lot of soil and a
1 per cent, sodium nitrate solution. The nitrate shows

^ Rhode Island Exp. Station, 3rd Anmial Report, 1891, p. 53; 4Jh
Report, et seq.

- Journ. Roy. Agric. Soc, 1897, p. 287; and subsequent years.

136 Fertilisers [pt. iii

no diminution in amount^ but some action nevertheless
goes on and calcium occurs in the solution. In conse-
quence ammonium sulphate is much in favour in tropical
countries and is used in the West Indies for the sugar
cane. Of course as soon as it has become nitrified it is
liable to sink to greater depths, but in an acid soU, or
wherever nitrification is not \^ery active, it remains in
the surface layers. Here it encourages a surface rooted
vegetation, and for this reason it is used on lawns where
only the fine shallow rooting grasses are desired.

This tendency to remain in the surface layers has
sometimes given sulphate of ammonia an advantage
over nitrate of soda on sandy soils not deficient in
lime^.

Commercial sulphate of ammonia contains about 20
per cent, of nitrogen ; it is the most concentrated of aU
these manures. Its pre-war price was about £13 per ton
f.o.r. : 1 per cent, per ton (or 1 unit) therefore cost 135.
and a poiuid of nitrogen in this form cost Id. During
the war its price was fixed by the Government : it varied
from £15. 5s. to £16. 15s. per ton. A little free acid is
usually present : if there is less than 0*025 per cent, the
sample is known commercially as " neutral."

Ammonium nitrate

This is much more concentrated than the ordinary
nitrogenous fertilisers, containing in the pure state no
less than 35 per cent, of nitrogen, m hich is more than
double the quantity in nitrate of soda. It has the dis-
advantage of being deliquescent and highly soluble, and
these properties interfered with its use in practice. It

^ A suitable test is given on p. 228.

* An instance is quoted in Bied. Centr., 1908, xxxvii. 585.

CH. vii] Nitrolim 137

proved of value in the Aberdeen experiments. Several
crystalline modifications exist, however, one of which
is sufficiently non-dehquescent to be of practical value
as a fertiliser. This can be stored and drilled and it
gave good crop increases at Rothamsted^.

Calcium cyanamide or Nitrolim'^

This fertiliser, like calcium nitrate, is made from air
and limestone. There are two stages in the manufacture :
first a mixture of calcium carbonate and carbon is heated
in an electric furnace to a high temperature, when cal-
cium carbide (CaCg) is formed; this is then heated in a
stream of nitrogen and gives calcium cyanamide
(CaCNa). It was first made at Piano d'Orte in Italy,
but now it is produced at Odda in Norway, Alby in
Sweden, at Niagara and elsewhere where great supplies
of water-power are available. A great increase in supply
is anticipated after the war. Calcium cyanamide is not
soluble in water and is not a direct plant nutrient. But
it decomposes in the soil with formation of calcium
carbonate and ammonia, which is then utilised in the
usual way. In consequence of the need for this pre-
liminary change calcium cyanamide is somewhat slower
in action at Rothamsted than sulphate of ammonia.
Being insoluble it is not at all likely to be washed out
from the soil, while the calcium carbonate formed on
decomposition is distinctly valuable. It is best applied
at or before the time of sowing so that decomposition
may proceed before the plant has grown ; when used as

1 Joiirn. Bd. Agrir. 1919, xxv. 13.32.

^ "Kalkstickstoff," in the German papers. There was another sub-
stance, not dissimilar, known as "Stickstoti'kalk," which, however, had
only a small local sale.

138 Fertilisers [pt. hi

a top dressing some samples have produced harmful
effects, but these do not invariably set in.

Special precautions are taken at the factory to de-
compose all the calcium carbide, and in the end the
cyanamide is sent out in very finely divided condition.
In this state it has proved objectionable to the labourers ;
during application to the land it gets into their eyes,
inouths and noses, and is the cause of some trouble.
Attem ts were made to overcome this by granulation
but they led to another difficulty. In presence of an
alkali cyanamide polymerises, two molecules joining
together to form one of dicyanodiamide, a substance
which in any large quantity is poisonous to plants and
also to the nitrifying bacteria, and in any case has
nothing like the fertilising value of cyanamide.

Pure calcium cyanamide contains 35 per cent, of
nitrogen, but the commercial product contains little
more than half its weight of the pure substance, the rest
cons sting largely of lime and some graphite. The com-
mercial product has therefore received a special name,
Nitrolim ; it contains usually 18-20 per cent, of nitrogen,
nearly the same as is present in sulphate of ammonia.

Comparison of these nitrogenous fertilisers

Table V gives the results obtained at Rothamsted in
comparative experiments with these various fertilisers.

At Cockle Park also nitrolim proved somewhat in-
ferior, but there was little to choose between nitrate of
soda and nitrate of lime^.

In 15 experiments at Aberdeen^ the nitrolim proved

» Cockle Park Bull. No. 18, 1912.

* Aberdeen and North "of Scotland College, Bulletin No. 13, 1909.
Trans. Highland and Agric. Society, 1909, 122-134. Journ. Soc. Cheni.
Ind. 1918, p. 146.

CH. VIl]

Comparative Values

139

equal to nitrate of soda or sulphate of ammonia, while
nitrate of lime was rather better, but owing to its hygro-
scopic nature it was less easy to handle. On an average
of all British experiments if the nitrogen of nitrate of
soda is valued at 100 that in sulphate of ammonia would
be 95 and in cyanamide 90. In experiments where each
substance is tested on one plot only, the results can only
be relied upon to within 10 per cent, in any one season,
or some 5 per cent, over several seasons. For finer work
it is necessary to repeat the plots 4 or 5 times in the
same field each year, and to ascertain from the results
exactly what is the error of experiment. The method of
doing this is described by Wood and Stratton in the
Journ. Agric. Science, vol. iii. p. 107, a paper which the
student should read.

Table V. Effect of various 7iitrogenous manures on
different crops. Rothamsted: yield per acre 1909-1914

Barley, 1909

Wheat, 1910

Hay
1914

Mangolds*
1914

Little Hoos

Little Hoos

Great

Great

Harpenden

Field

Grain Straw

Grain Straw

Field

bush.

lbs.

bush.

lbs.

cwts.

tons

No nitrogen

28-7

2619

15-4

1526

17-6

17-8

Nitrate of soda

48-1

3882

27-0

3760

25-9

— .

Sulphate of ammonia

49- 1

3517

24-6

2964

—

—

Nitrolim

45-2

3976

22-4

2343

21-5

18-4

Nitrate of lime

46-2

4449

20-6

3618

—

210

Nitrate of ammonia

~

—

18-7

* Twelve tons of dung per acre was appUed to all the Mangold plots.

CHAPTER VIII

PHOSPHATES

Practically all of the clay lands of the country and
many of the other soils stand in need of phosphates, and
the higher the standard of farming the greater is the
amount required. There are three main sources from
which supplies are drawn : bones, superphosphate, and
basic slag.

Bones

Bones have long been applied as manure in isolated
parts of the country, but they were not commonly used
until the beginning of the 19th century. Such remark-
able results were then obtained in certain districts, e.g.,
in Cheshire, that the demand became very great, and
the rather large accumulations of the past in various
parts of the world had to be drawn upon to satisfy it.
The demand stiU continues ; the butchers' shops, meat
markets and marine store dealers of the great cities are
ransacked to keep up the supply. In modern practice
the bones are sent to the works, put on to a perforated
band and sorted; clean shank bones are picked out for
cutlery, hard bones for glue making and the remainder
for crushed bone : the separate batches are steamed at
low pressure (15-20 lbs.) to remove fat, nowadays a
valuable commercial product. In some works the bones
are degreased with benzene, and this process is more
efficient than steam, so that the residual bone meal is
richer in nitrogen and in phosphate.

CH. VIIl]

Bone Manures

141

Bone meal. The bones intended for this purpose are
then crushed and sorted into half inch bones, quarter
inch bones and bone meal.

Steamed bone flour. The bones intended for glue, and
the ends of the cutlery bones, are crushed and again
steamed but this time at a higher pressure (50 lbs.),
when most of the nitrogenous constituents are extracted
as gelatine or glue. The residue can now be got into a very
fine state of division and is sold as steamed bone flour.

Dissolved or vitriolised bones. These are made by
treating bones with sufficient sulphuric acid to dissolve
about half of the phosphate. The product is usually
somewhat sticky, and has not the finish of a well-made
superphosphate. The following table gives the com-
position of various bone manures, but as the material
is very variable the figures are to be considered as
approximate only. Raw bones are still used in the Wolds
of Yorkshire and in certain other districts but not
generally elsewhere.

Equivalent

Equivalent

Nitrogen

to
ammonia

P2O6

to tricalcic
phosphate

Raw Englif?h bones

5

6

22

48

Bone meal

3-5-4-5

4-2-5-4

20-25

43-55

,, a usual analysis

3-75

4-5

20-6

45

Steamed bone flour

1-2

1-2-5

25-32

55-69

Dissolved bones

2-3

2-3-3-8

15-16

33-35

Bone meal usually acts best on soil rich in humus or
soils lacking in lime; it is not very satisfactory on cal-
careous soils. At Rothamsted it gave good returns for
spring wheat, barley and swedes, and also at Saxmmid-
ham, but in the Cockle Park^ and Aberdeen experiments

Cockle Park Bull. No. 37, Davy Houses Field; Aberdeen Bull. No. 3.

142 Fertilisers [pt. hi

it has not proved as useful as basic slag or superphos-
phate and has not justified its popularity.

Steamed bone flour contains less nitrogen, but so far
as the phosphate is concerned it has the advantage that
it is very finely divided and can readily be distributed.
It gives good results on light alluvial loams.

Dissolved bones resemble superphosphate in their
action but are on the whole more expensive and less
satisfactory.

Superphosphate

On May 23rd, 1842, Lawes patented his process for
manufacturing superphosphate and thus founded the
artificial fertiliser industry which has since attained
enormous dimensions. The principle of the process is
very simple: rock phosphates (themselves of no great
fertilising value in this country) are treated with sul-
phuric acid so as to convert the tricalcic phosphate
Ca3(P04)2 into the more soluble compound to which the
formula Ca(H2P04)2 is assigned: in addition calcium
sulphate is formed. The following is the usual expres-
sion of the reaction ; it is not, however, strict^ correct :

Ca3(P04)2 + 2H0SO4 = 2CaS04 + Ca(H2P04)2.

The mixture of calcium sulphate, monocalcic phos-
phate and some free phosphoric acid^ constitutes the
superphosphate. No separation is attempted, and the
calcium sulphate or gypsum is left in : it not only docs
no harm but has itself some fertilising value and indeed
was much used in the past: it also serves to get the
superphosphate into a dry condition because it absorbs
water very completely. The process has attained a con-
siderable degree of perfection, and allows of the pro-
^ J. H. Coste, Journ. Soc. Chem. Ind. 1897, xvi. 195.

CH. VIII j Superphosphate 143

diiction of a high grade product, finely powdered and
dry, free from many of the defects of the older samples.
The world's annual production was before the war about
10 million tons.

The rock phosphate comes largely from Northern
Africa and it contains other substances besides calcium
phosphate : the resulting superphosphate is therefore not
entirely constituted as shown in the equation. The rock
sometimes contains calcium carbonate, in which case an
additional proportion of calcium sulphate is formed. On
an average 10 tons of rock phosphate give rise to about
18 tons of superphosphate instead of the theoretical 17.

It has been found convenient to standardise the
various grades of superphosphate and sell them on a
definite basis. The amount of soluble phosphate is
determined by analysis as PoOg and the figure is then
calculated as tricalcic phosphate. Thus the ordinary
grade contains about 12 per cent. P2O5 soluble in water;
this figure is then multiplied by 2-18 to convert it into
tricalcic phosphate Ca3(P04)2. Both figures are con-
ventional in that superphosphate consists neither of
P2O5 nor of Ca3(P04)2, but either figure does very well
to express the amount of phosphate soluble in water.
The following grades are now obtainable:

Fixed price
f.o.r.
" 26 p.c. soluble" equivalent tolI-8 p.c. PgOj £6.
"30 p.c. soluble" „ 13-6 „ £6.10.9.

"35 p.c. soluble" ., 16-0 „ £7. 10s.

± a sum not exceeding 7s. 6rf. according to time of purchase.

The student must realise very clearly that the ex-
pression "30 per cent, soluble" does not indicate the
presence of 30 per cent, of anything in the manure itself.

Price per

unit of

jhosphate

P2O5

45. Id.

10s. Id.

4s. U.

9s, U.

4s. U.

9s. 4d.

*9^

144

Fertilisers

[PT. Ill

It simply means that the soluble pho-phate present
would amount to 30 per cent, ij it were there as tricalcic
phosphate. But it is not. and the only justihcation tor
this rather cumbersome method of expression is that all

4C§pl^

T

Plot 1 3 5

Fig. 30. Effect of fertilisers on swedes (Agdell field.
Rothamsted, 1912.)

Plot 1. Complete manure — phosphates, potash and nitrogen
compounds.

„ 3. Incomplete manure — phosphates and potash but no

nitrogen compounds.
„ 5. No manure.

manures are worked out on the same basis, to which
everybody has become accustomed. The more concen-
trated grades save freight; the others supply a larger
amount of gypsum which under some circumstances has
distinct manurial value.

CH. viii] Effect on Crops 145

Superphosphate has two remarkable effects on the
crop: it favours root development in the early stages
of plant growth, and it hastens maturity in the later
stages. It is specially useful for swedes and turnips,
and gives returns even when the soil seems rich in
phosphates. Fig. 30 shows the results obtained at
Rothamsted: unmanured turnips failed to swell and
remained like radishes, turnips manured with super-
phosphate and potash swelled to a considerable size
even without nitrogenous manure, while when this was
added still further growth was obtained.

After a wet winter a dressing of 3 cwt. of super may
considerably assist the young winter corn to form roots.
Nitrate of soda or sulphate of ammonia should be given
at the same time.

Its effect on maturity is well seen on the barley plots
at Rothamsted. Wherever phosphates are withheld the
crop ripens badly : where they are supplied it ripens well.
Indeed cases are on record elsewhere where the ripening
has gone on too quickly, so that the crop has suffered in
consequence.

At Rothamsted the barley on the permanent plots
stands greatly in need of phosphates: the results are
plotted in Fig. 31.

Phosphates also increase the feeding value of fodder
crops and for this reason must be liberally used wherever
recourse is had to folding or where many head of stock
are kept. Addition of superphosphate to the seeds ley
often leads to improvement in the sheep grazing the
aftermath. ,

In horticultural practice superphosphate proves very
valuable for inducing hard growth in plants that are
becoming too sappy.

R. s. 10

146 Fertilisers [pt. hi

Even small dressings have produced marked all-romid
improvement on soil very deficient in phosphates. The
most striking examples are found in Austraha and have
been investigated at the Roseworthy Agricultural Col-
lege^; good instances also occur in Cardiganshire,
Striking effects are also produced in the Fens.

Grain per Ac re, lb

Phosphoric Acid

and

Potash.

Straw per Acre, lb.

Fig. 31. Effect al phosphates and of potash on the yield of barley.
(Hoosfield, Rothamsted.) (Average 60 years, 1852-191 1.)

The columns represent total produce per acre while the figures in the
diamond spaces give bushels of grain and cwts. of straw per acre.

Superphosphate is soluble in water but it is rapidly
precipitated in the soil and only very small quantities

» See especially 4<A Report, 1909-11.

CH. VIII J Basic Slag 147

are found in the drainage-water: practically the whole
of the superphosphate added to the Rothamsted soils
during the past 60 years and not taken by the crop still
remains in the soil. It is sometimes described as an acid
manure; the statement may at one time have been
correct but it is now misleading, a well-made sample
contains no more than 3 or 4 per cent, of acidity. There
is no evidence that it causes the soil to become acid : the
Broadbalk plot manured with superphosphate does not
lose its lime any more quickly than the corresponding
plot without superphosphate. It has no bad effect on
the texture of the soil, on the contrary it not infre-
quently causes an improvement.

Superphosphate ought always to be in good mechani-
cal condition so 'that it can readily be drilled.

Basic slag ( formerly called basic cinder, Thomas''
phosphate powder, etc.)

Basic slag is a by-product in the manufacture of
steel. The first stages lead to the production of pig iron
which contains quantities of silicon, carbon, sulphur,
phosphorus, etc. In the second stage these substances
have to be largely removed, and this is done by heating
the molten metal to a high temperature in presence of
air, when they are aU oxidised.

Two processes are in use for effecting this oxidation.

The older one, adopted in 1879, is the Bessemer pro-
cess ; the molten pig iron is run into a pear-shaped vessel
known as the converter, and air is blown through it.
The changes to be brought about require a high tem-
perature, which is mainly obtained by the combustion
of the phosphorus, silicon, etc., contained in the pig iron
itself. It is therefore to the advantage of the steel maker

10—2

148 Fertilisers [pt. hi

to have sufficient phosphorus present ; if the ore does not
contain enough for the purpose foreign ores rich in
phosphorus, or Belgian phosphates, are added in the
blast furnace. All the phosphorus goes into the pig iron
and when this is blown in the converter a slag is "obtained
containing phosphate equivalent to 40 per cent, or more
tricalcic phosphate.

The more recent method is known as the Open Hearth
Process, and being more convenient to the steel makers
it seems likely to displace the Bessemer process; im-
fortunately for the agriculturist it does not produce so
useful a slag. The p'ig iron is heated in a furnace by
superheated producer gas; the heat is therefore quite
independent of the amount of phosphorus present, and
there is no inducement to the open hearth steel maker
to ensure a high, or indeed any, phosphorus content in
his pig iron. The average phosphoric irons produced
in England contain only 1-5 per cent, or less phosphorus,
and when worked in the open hearth furnace yield a
slag containing only 7 to 14 per cent, phosphoric acid
(PgOg) equivalent to 15-4 to 31 per cent, tricalcic phos-
phate of lime.

Further, the open hearth slags are not usually as
readily soluble in citric acid as those yielded by the
Bessemer process. This happens particularly when the
pig iron contains much sulphur. An excess of lime is
required to remove the sulphur, and as this makes the
slag infusible, fluorspar or calcium chloride is added to
increase the f usibihty. This treatment has the effect of
rendering the slag insoluble in citric acid, hence the slags
finally produced are more or less insoluble according
to the amount of lime and flux added.

There are three classes of basic slag available :

CH. viii] Grades of Slag 149

. 1 . Bessemer slag, containing phosphoric acid equiva-
lent to 40 per cent, or more of tricalcic phosphate, and
largely soluble in 2 per cent, citric acid; usually 80 per
cent, of the total is guaranteed to be soluble.

2. Basic open hearth slag containing less phosphoric
acid, equivalent to 15 to 31 per csnt. tricalcic phos-
phate largely soluble (80 per cent.) in 2 per cent, citric
acid, the first pourings being richer than the last.

3. Basic open hearth slag made by the use of lime
and fluorspar, containing as much phosphate as the
poorer members of the preceding class but only slightly
soluble (20 per cent, or less) in 2 per cent, citric acid.

When basic slag was first obtained in the Bessemer
converters in 1879 its fertilising properties were not
recognised; not till John Wrightson in 1884 and 1885
made his field experiments at Ferryhill and at Downton,
and Paul Wagner in 1885 began his systematic pot
experiments at Darmstadt, were agriculturists aware of
its value. It gradually came into use and within 4 or 5
years could profitably be adulterated with mineral
phosphates, to detect which Wagner devised the well-
known citric acid test that, with certain modifications,
has remained in force ever since.

The more modern open hearth slags have been tested
in Northumberland by Gilchrist, in Essex by Scott
Robertson, in Devon by Dutton and at Saxmundham
by Oldershaw. The second class have proved substan-
tially equal in fertiliser value to the old Bessemer slags.
The third class have also proved much more effective
than was first assumed from their low solubility in citric
acid. Where the growing season has been sufficiently
long these slags are approximately as useful as the others
in spite of their low solubility. Where the growing

150 Fertilisers [pt. hi

season is shorter or an early start more necessary the
high soluble slags have proved more effective.

Basic slag is sometimes said to contain 22 to 44 per
cent, of tricalcic phosphate, but this is incorrect: the
actual nature of the phosphorus compound is not yet
known but it is probably a complex silico-phosphate^ :
the method of expression as tricalcic phosphate is con-
venient as it allows instant comparison with other phos-
phatic fertilisers. It contains a certain amount of free
lime, usually about 2 per cent., which gives a distinct
alkaline reaction, in addition a considerable quantity of
the combined lime can probably act as a base in the
soil (see p. 219).

Basic slag is not soluble in water but it dissolves in
carbonic acid which occurs in the soil-water, and there-
fore readily comes into solution in the soil. The action
is hastened by its fine state of division, at least 80 per
cent, being guaranteed to pass a sieve with 100 meshes
to the linear inch.

It has given remarkable results on clay grass lands,
and has probably been the cause of greater improve-
ment on these than any other single factor, its action
being to bring on the white clover which then so in-
creases the nitrogenous organic matter of the soil that
greater growth of grass becomes possible. As its effect
is at a maximum when the herbage is most scanty it is
best to begin with a heavy dressing, say 8 to 10 cwt.
per acre in the first year, followed by 5 cwt. at a later
date. This is an apparent exception to the general law

1 Morison (Journ. Agric. Science, 1909, ni. 161-170) shows that it is
probably a compound of the type (M0)6M'0, SiOa, P2O5. He actually
found (CaO)5FcO, SiO.,, PoOg. There is no evidence for the statement
often made that basic slag is a tetra -basic phosphate. A further paper on
the subject is by Krol, Journ. Iron and Steel Institute, 1911, p. 126.

CH. viii] Slag on Grass Land 151

discussed later (p. 214) according to which the largest
return per unit quantity of manure applied is obtained
from small dressings: it happens because the effect of
slag is in a large measure indirect, the improvement
arising from the stimulation of the clover. Experiments
at Cockle Park^ and elsewhere have demonstrated the
great increase in feeding value of the herbage treated
with slag. It has also had a remarkable effect on the
downland pastures of Sussex and Hampshire, seen for
example at Sevington in Hampshire^, and on Prof.
Somerville's farm, Poverty Bottom, at Newhaven^.
The older practice was to apply it in autumn or winter
but later work has shown that spring and even summer
dressings are also good.

In dry situations, however, it proves less effective,
e.g., on some of the Hertfordshire gravels and on the
downland of East Kent. Sometimes the failure is due
to lack of potash, which can be remedied by addition of
kainit*.

It is valuable on arable land for swedes and turnips
wherever there is any tendency to finger and toe, and
it also increases the feeding value of the roots.

The fixed price of slag is :

Total Equivalent
phosphate to P2O5

Price
f.o.r.5

Price per unit
Phosphate P2O3

20 per cent. 9-1

68s.

3s. 5d. Is. Qd.

34 per cent. 15-5

88s.

2s. Id. 5s. M.

Over 3| million tons are produced each year.

^ These are summarised in Prof. Somerville's paper, Journ. Bd. ofAgric,
Supplement, Jan. 1911.

2 Journ. Bath and West Society, reported annually, 1901 onwards
= Journ. Bd. of Agric. 1918, xxiv. 1186.

* E.g., see Woburn Experiments, Journ. Roy. Agric. Soc, 1907.
^ See footnote, p. 131.

152 Fertilisers [pt. hi

Comparison of basic slag and superphosphate. On
heavy clays, on downland pasture and in wet situations
slag is generally better than superphosphate. For roots,
potatoes, hops and other short season crops superphos-
phate is usually better than slag. In Hendrick's swede
experiments! at Aberdeen there was little to choose
between them, though for equal amounts of phosphate
apphed superphosphate gave on the whole shghtly
larger increases in crop,' but where finger and toe was
prevalent it required the addition of lime. In the Irish
experiments equal weights of basic slag and super-
phosphate gave approximately equal results^. Some of
the Yorkshire experiments giving the same result are
set out on p. 162. From these and other experiments we
may conclude that the two fertilisers are nearly equally
effective and that the choice between them must turn
on special circumstances such as climate, the wetness,
heaviness, etc., of the land. It is not uncommon or un-
wise to apply both to the soil — separately, not mixed.

Other phosphates

From time to time other attempts have been made to
utilise natural phosphates by converting them into more
readily soluble compounds, the most interesting of which
are those of Wilborgh and of Palmaer, both of the Poly-
technic Institute of Stockholm. Large quantities of im-
pure natural phosphates are obtainable from the North
of Sweden, which Wilborgh attempted to utilise by
fusing with sodium carbonate. The product was good,
but too costly. Palmaer adopted an electrolytic method,

1 Aberdeen College, Bull. Nos. 1, 4 and 8, 1904, 1906, 1907. Also
Trans. Highland and Agric. Soc., 1906.'
* Journ. Dept. Agric, Ireland, 1913.

CH. viii] Mineral Phosphates 153

and acted on the phosphate with the acid solution
collecting round the anode during the electrolysis of
sodium chlorate, then precipitated with the alkaline
solution from the kathode, and finally filtered to re-
cover the sodium chlorate which was once more electro-
lysed. The material is found to be satisfactory^.

Sometimes mineral phosphates themselves are ground
and sold as fertilisers but no great quantities are used
in this country. Beneficial results have been obtained
in many parts of the United States, especially on sour
derelict land^. Moorland soils also frequently respond to
mineral phosphates. Neither of these results, however,
affords much guidance as to what other soils will do ; in
particular, moorland soils respond more than others to
fertilisers of low solubility. Increased crops, however,
have been obtained at Cockle Park in Essex^ and also
at Aberdeen where dung was applied, but not other-
wise*. There is some evidence that finer grinding would
lead to better results.

^ Von Feilitzen, 8th Congress, Applied Chemistry, vol. xv. p. 85; also
Journ.fu) Landw., 1910, p. 33, and 1911, p. 371.

^ A summary of the American investigations is given in Journ. Agric.
Research, 1916, vi. 485.

3 Guide for 1913, pp. 39, 40.

^ Aberdeen Bull. No. 10, 1909. For a general summary of the effects
of the mineral phosphates see the author's Notes on Fertilisers, Journ.
Bd. of Agric, Feb. 1917, and May 1917.

CHAPTER IX

POTASSIC FERTILISERS

The system of agriculture long in vogue in this
country consisted in selling grain and meat from the
farm but returning the straw to the land in the form
of manure. As the straw contains a large proportion
of the potash while the grain and meat contain much
phosphate, it is evident that the tendency of the system
M^as to keep the potash on the farm and to reduce to
a minimum the need for buying potassic fertilisers.

But with the more varied types of cropping of recent
times, and above all the extended growth of potash-
needing crops like mangolds, potatoes, and, on the
Continent, sugar beet, there has arisen the necessity for
applying potash to the soil and for this purpose large
quantities of potassium salts were imported prior to the
war. These all came from Stassfurt in Prussia, and it
was supposed that no other deposits of economic im-
portance existed elsewhere. The shutting off of these
supplies during the war, however, has led to a systematic
and not unsuccessful search for other sources of potash.
Natural deposits have been investigated in Alsace, Spain,
the AVestern United States, and elsewhere.

In tliis country blast furnace flue dust has been ex-
ploited: it contains potassium compounds deriv^ed from
potash which has volatilised from the fuel, ore and flux^.
The furnace gases are collected as completely as possible

^ Journ. Bd. Agric. 1917, xxiv. 526, 852, also Journ. Soc. Chem. Ind.
1918, xxxviT. 222 T.

CH. IX] Flue Dust 155

because they contain so much combustible gas that
they can be used for heating the air blast and the steam
boilers with which to run the works.

In order that these gases should not clog the burners
they must be freed as far as possible from the dust
mechanically carried over. They are therefore either
washed through water or passed into a dust catcher, a
large box hung with sacks in which the dust can settle
and from which it can be removed as frequently as neces-
sary. Another method consists in causing the gases to
pass between electrified plates when the dust is com-
pletely thrown down. Three grades of dust are obtained :

1. The black dust from the main collectors, con-
taining the soot and about 3 per cent, of potash (KgO)
mainly as sulphate and silicate;

2. A red or whitish brown dust collected from the
boilers or stoves which is derived from the black dust
by the burning away of most of the soot : it is therefore
richer in potash and contains some 15 per cent, of KgO,
again mainly as sulphate and silicate ;

3. An intermediate grade.

More potash volatilises if a certain amount of salt is
added to the charge in the furnace: in this case it
appears as muriate.

Some samples of flue dust contain cyanides and sulpho-
cyanideswhichwouldbe harmful if present inlarge propor-
tions. Tests should alwaysbe made for these substances^.

^ A simple test is as follows. Place about 1 gram of the dust in a
200 c.c. flask with 100 c.c. of water, (clean tap water will do,) and shake
for half a minute. Filter 10 c.c. into a test-tube, add a few drops of dilute
sulphuric acid (1 in 4) and 1 c.c. of iron alum solution. If nothing happens
the material can safely be used. If the solution turns red sulphocyanides
are present; if it turns greenish brown ferrocyanides are present : in neither
case should the dust be used until it has been examined by an analyst.

166

Fertilisers

[PT. Ill

Some of the flue dust is now being lixiviated and made
to yield muriate or sulphate of potash.

Raw wool contains a fair amount of potash which is
removed during the washing process to which it is sub-
jected at the mill. About 500,000 tons of wool are dealt
\vith annually in Yorkshire; the potash content varies
from very little in wool washed on the farms up to about
3 per cent, or more expressed as KgO in unwashed wool.
It is impossible to estimate the amount obtainable from
this source owing to the paucity of analytical data, but
it must be fairly considerable. The extraction of potash
used to be carried out in the wool-washing factories in
the Roubaix district of France and also in Belgium, and
experiments on the subject are now being done in this
country^.

Bracken ash has aroused considerable interest; it
contains the following quantities of potash at various
stages of its growth^ :

Percentage of potash in the ash

lbs. of potash (KnO) obtainable
from an acre of bracken
(approx. estimate only)

Dundonald
(Ayrshire)

Aber
(N. Wales)

Harpenden
Common

Dundonald

Aber

Harpenden

June 1st

July Lst

Aug. 1st

Sept. 1st

October

Withered stems and
leaves from last year:
exposed throughout
the winter

53
47
42
37
21

51
39
32

54
47
41
34
29

2

152

264

289

225

40

180

13
32
56
60
60

5

1 J. p. White, Journ. Textile Institute, 1912, iii. 294-302. A. F. Baker,
Journ. Leeds Univ. Textile Assoc, 1915, iv. 69.
* Journ. Bd. Agric. 1918, xxv. 1.

Bracken and Wood Ashes

157

CH. IX]

The ashes of young plants are rich in potash and in
bjT^gone days a considerable amount used to be ex-
tracted from this source: unfortunately^ the percentage
falls off as the plant becomes older and larger so that
the amount of potash obtainable does not increase pro-
portionately to the growth.

Fig. 32. Effect of potassic fertilisers on mangolds.

(Barnfield, Rothamsted.)

Left-hand heap — Superphosphate and nitrogenous manure, no

potassium salts.

Right-hand heap — Superphosphate, nitrogenous manure and

potassium salts.

The ash of young wood contains up to 35 per cent, of
potash, that of older wood about 15-25 per cent. All
dried vegetation loses potash on exposure to weather;
the ash obtained by burning brushwood, hedge trim-
mings, etc. contains only about 10 per cent, of potash,
and much of this is lost by the washing of the rain.

158 Fertilisers [pt. hi

In the United States considerable attention has been
devoted to the possibiHty of extracting potash from

Tons per
acre
25

«

*f . * • ■

*^0

■ :•■.'..•.

1 5 —

'. '•' ' ."

10

' ' V •

M

wa

9/
i

.*'.*■•■

No Super Super Super

minerals only and potassium

potassium and
salts magnesium
salts

Fig. 33. Effect of mineral manures on the yield of mangolds already

receiving nitrogenous manure (ammonium salts and rape cake).

Barnfield, Rothamsted. (Roots, tons per acre, average 37 years,

1876-1912.)

feldspar especially when carried out as part of the pro-
cess for manufacturing Portland cement.

CH. ix] Effects on Crop Production 159

Kelp has also been examined and also certain natural
deposits in the Western States. From one source or
another no less than 32,000 tons of potash (KgO) was
produced in the States in 1918.

Certain minerals, notably feldspar, phonolite, etc.,
have been suggested as fertilisers, but they proved in-
effective in trials made at Woburn. Biotite and nephelin
were more successful in Prianischnikow's experiments.

It is only since the "sixties" that the Stassfurt
salts have been on the market, but the demand grew
so rapidly since 1900 that nearly 10 million tons per
annum of the crude salts representing approximately
one million tons of K2O were sold before the war,
mainly for agriculture. Three salts were in common use
here: sulphate of potash, muriate of potash, and kainit.
The Alsatian deposits occur in the plain north of Mul-
house ; they are estimated at 300 million tons of salts
containing on an average 22 per cent. KgO^.

Potash is particularly needed for certain special crops
like mangolds (Figs. 32 and 33), potatoes and flax; in-
deed in this country it is usually associated with dairy
and potato farming. A usual dressing is 2 cwt. of
muriate or sulphate of potash for potatoes or 4 cwt. of
kainit for mangolds. Also, it is often effective on grass
land, especially on thin soUs, and on leguminous crops.
It may be needed for other crops as the standard of
farming rises and the yields are forced up : the natural
supplies of potash in the soil are not always sufficient
for the higher crops that ought to be obtained. Thus
on the Rothamsted barley plots phosphates give a con-

^ The Stassfurt deposits are described in The Potash Salts, their Pro-
duction and Application, Dr Groth, Lombard Press, Londoji, and the
Alsatian deposits in Journ. Soc. Chem. Ind. 1918, xxxvn. 291 T.

160

Fertilisers

[PT. Ill

siderable increase in yield, but a still further increase is
obtained by suppljdng potassium salts in addition
(Table VI).

Table VI. Effect of manures on the yield of barley.
Rothamsted: average 60 years, 1852-1911

Dressed grain

Straw

Treatment of barley

bushels per acre

cwts. per

Sulphate of ammonia only

25-5

14-7

„ „ „ + potash

28-0

16-9

„ „ „ + super

38-2

22-0

„ „ „ + super + potash 41-5

25-0

Another instance is afforded at Saxmundham (Table
VII). The soil is heavy and potash was not expected to
give a return, nor did it so long as the yields were low.
But directly phosphates are added the yield goes up and
the potash-needing plants — beans, peas and lucerne —
can now increase beyond the capacity of the soil supplies
of potash. Fresh additions of potash are therefore neces-
sary for these crops, but not, however, for barley or
wheat.

Table VII. Effect of potassic manures on croups.
Saxmundham : average yields 4 years, 1910-1913

Lucerne^

Beans and
Peas

Roots

Barley

Wheat

Corn

Straw

Grain Straw

Grain Straw

cwt.

bush.

cwt.

tons

bush. cwt.

bush.

cwt.

No manure

25

20-8

14-3

6-7

21-3 17-5

19-4

20-5

2 cwt. nitrate of soda

25

22-9

16-8

5-3

26-5 26-0

23-2

30-3

2 cwt. each nitrate

of soda and super-

phosphate

58

31-7

26-3

15-2

34-1 280

29-2

32-8

2 cwt. each nitrate

of soda, superphos-

phate+1 cwt. mu-

riate of potash

62

350

28-1

16-4

34-2 29-7

25-3

340

1 6 years, 1903-1908.

CH. ix] Effects on Plant Growth 161

Whenever land of any kind has been improved and made
to yield higher crops a trial should always be made to
see if potash is needed.

Light sandy and moorland soils respond considerably
to dressings of potash, except sometimes where farm-
yard manure is used^. It is because of the wide occurrence
of these two types of soil in North Germany and of
moorland soils in Sweden that potash is so much used
in those countries ; the demand is still further increased
by the great quantity of sugar beet grown. Light chalky
soils also respond to potash. Although all three salts
are easily soluble they are readily precipitated in the
soil and only wash out with difficulty, so that the
drainage-water is practically free from potash.

The main effects of potash on the plant are three. It
facihtates either the production or the translocation of
sugars and starches from the leaf ; hence its value for
sugar- and starch-making crops like sugar beet, man-
golds and potatoes.

It stiffens the straw of cereal crops and of the grass
tribe generally: at Rothamsted the wheat and grass
crops growing on the plots deficient in potash tend to
become laid, especiallj^ in bad seasons.

Further, it enables the plant to withstand adverse
conditions of soil, climate or disease, etc. The plants
well supplied with potash at Rothamsted do better in
bad years — whether of wetness or of drought — than the
others: they are also more resistant to rust and other
diseases. On the potash-starved plots the grass not only
becomes laid, but is also liable to attacks of the fungus
EpicJiloe, and in addition the seed heads are often
barren; the mangolds are badly attacked by the fungus

1 See Cockle Park Bui. No 19, p. 51.
R. S. 11

162

Fertilisers

[PT. Ill

Uromyces betae; the wheat is always subject to rust and
the tips of the leaf begin to die early in the season and
then the edges turn yellow for some distance down.
Elsewhere also dressings of potash have enabled plants
to withstand pests: flax in Ireland, tomatoes in glass-
house culture, spring oats affected by eelworm have all
furnished cases in point. Potash manures also tend to
counteract rankness of growth and therefore find valu-
able apphcation for glasshouse and nursery work.

In farm practice considerable quantities of potash are
supplied in dung and liquid manure where this is used
(p. 177). Potassic salts are given usually to potatoes,
mangolds or flax: the cereals in the rotation can then
very well take up the unused material. On the whole
kainit is better for mangolds while the sulphate or
muriate is better for potatoes and flax ; between sulphate
and muriate, however, there is little to choose^. Where
potash is wanted for grass land kainit is perhaps the
better and on the whole cheaper: the results of the
Yorkshire experiments ^ which are typical of many
others are given in Table VIII.

Table VIII. Yorkshire experiments on meadow hay.

No manure
Nitrate of soda

Cwts. per ac)

( super

Nitrate of soda + \ steamed bone flour
V. slag

Nitrate of soda + phosphates + potash as

' sulphate
muriate
kainit

Garforth
32
43
44
43
44
43
45
42

Horton
36
43
45
45
45
49
51
52

1 loth Annual Report, Durham Coll., 1902, p. 30; Journ. Irish Dept
Agric. XIII. 254; Leeds Bull. No. 58, pp. 19 and 20.
* Ouide to the Garforth Experiments, 1913, p. 3.

CH. ix] Prices 1 63

At Garforth the potash has usually given no return;
at Horton, however, distinct increases have been
obtained.

In glasshouse practice sulphate of potash is generally
considered better than kainit.

The muriate and sulphate are single potassium salts
but kainit is not: it is a mixture blended to constant
potash content containing sodium and magnesium salts
as well which have distinct fertilising value although
they are not as effective as potash. Dressings of potash
and particularly of kainit have occasionally reduced the
crops, apparently because interaction with the calcium
carbonate in the soil gives rise to potassium carbonate
which has a bad effect on the soil texture^.

The composition and prices of the three manures were
before the war:

Containing

potassium

equivalent to

Sulphate of potash 48-5 % of K2O

Muriate of potash 45 -,

Kainit 12-5 „

During the war sulphate of potash rose to £50 per ton
at which price it could hardly be profitable except for
potatoes and flax, and in special cases for other crops on
light soils.

Flue dust, however, was obtainable at much cheaper
rates :

Price

per ton

f.o.r.

Price per

unit of

KgO

£11

4s. 6^d.

£10. 7s. Od.

4i. Id.

£2. 12s. Od

4s. 2d.

Percentage

of potash

(K^O)

Price per

ton f.o.r.
in bags

Grade 1 2|-3i
,, 1 a 3i-5i
„ 2 5^91
„ 3 91-13

37s. &d.

46.0. M.

60s. Qd.

100s. U.

mce is afforded at Garforth :

see Guide, 1913, p. 20

11—2

164 Fertilisers [pt. hi, ch. ix

Salt as manure. Salt acts in two ways: it liberates
potash from the soil, and it economises the use of potash
in the plant. It can therefore be used with advantage
wherever potash is known to be needed. It has proved
useful for mangolds on all soils, and on light land for
grass and for wheat ^.

^ Norfolk Chamber of Agric. Expts.

CHAPTER X

MANURES SUPPLYING ORGANIC MATTER:
FARMYARD MANURE

Organic matter is a general expression used to denote
substances of animal or vegetable origin in contradis-
tinction to the nitrates, phosphates and potassium salts
which are termed inorganic. It contains carbon, hydro-
gen and oxygen and is combustible : this property is used
in practice for distinguishing it from the inorganic
matter of soils or fertilisers which is usually non-com-
bustible.

Organic matter differs in twoimportant directions from
the mineral substances studied in the preceding chapters.
Nitrates, phosphates, and potassium salts are directly
assimilated by plants; organic matter apparently is
not, and it derives no fertilising value from its three
characteristic components but only from any nitrogen,
phosphorus or potassium it may contain. Before these
elements can be utilised by the plant, decomposition
must take place in the soil; this is effected by moulds
and bacteria, and gives rise to ammonia, carbon dioxide
and certain complex residues grouped together as
humus. The fertilising value of the organic matter de-
pends very much on the rate at which this decomposition
proceeds, which in turn is determined by the bacterial
efficiency of the soil and by the nature of the substance.
Protein and the simpler compounds such as urea are
rapidly decomposed to form ammonia in the soil, but
the more complex substances which occur in straw,

166 Fertilisers [pt. hi

wool, etc., break down more slowly. Field experiments
have shown that the eflfect of ammonia only lasts for one
season, any excess not taken by the plant being washed
out during winter. The easily decomposed substances
therefore only act for one year: they are called quick
acting manures. The more complex substances decom-
pose more slowly and last more than one year : they are
called slow acting or lasting manures. There is no
special virtue in a slow acting manure: one pound of
nitrogen will only jdeld the same amount of ammonia
whether the decomposition process takes weeks or
years: indeed there is the disadvantage that a slow
acting manure represents capital locked up while the
quick acting manure gives a quick return. It will be
seen below that all the protein substances — dried blood,
rape cake, guano, the cake fed to animals — are quick
acting and may last only one year, while straw and wool
{i.e., shoddy) last longer in the soil.

The second great distinction between organic matter
and artificial fertilisers lies in their effect on the soil.
Artificial fertilisers have comparatively little action as
a rule ; organic matter, on the other hand, causes great
improvement in physical condition and in water-holding
capacity. Some of the Rothamsted plots receiving no
organic fertiliser have now so bad a texture that diffi-
culty is experienced in getting a tilth, and crops Uke
roots that are dependent on a fine tilth suffer accord-
ingly: cereals, however, are not affected. On the light
soils of Norfolk farmyard manure is almost indispens-
able, no mixture of artificial fertilisers having been
foimd so effective^ ; bullock feeding is therefore largely
practised to ensure ample supplies. On the light soils of

>■ Norfolk Chamber of Agric. Expts.

CH. x] Value of Organic Matter 167

Durham and Northumberland artificial fertilisers gave
considerably poorer yields than dung, or dung and
artificials^. Extreme cases arise where artificial fer-
tilisers are of practically no value while the organic
manures lead to considerable increases in crop : such
cases are not common in this country, but they are not
infrequent in subtropical conditions, as for example in
Madras, Java, etc. Here neither nitrates, phosphates
nor potash give appreciable crop increases while the oil
cake residues have considerable fertilising value-.

Organic matter cannot be regarded as necessary for
plant nutrition however desirable it may be from the
point of view of soil management. Large crops of wheat,
barley, mangolds and grass are regularly grown at
Rothamsted on land wliich for 70 years has received no
organic manure and the crops show no signs of falling
off. A strict comparison was made by Hansen on a light
loam and on a sand at Askor (S. Jutland) where farm-
yard manure was compared with a dressing containing
equal amounts of nitrogen, potash and phosphates in
the form of artificials (nitrate of soda, superphosphate
and kainit) and almost always gave poorer results^.

But if organic matter is not needed by the crop it
is commonly required by the soil: and experiments all
over the country have shown that the best economic
results are obtained by a judicious combination of
artificial fertilisers with organic manures.

Farmyard manure. Farmyard manure consists of the

1 Armstrong Coll. Bull. No. 10, 1915.

^ See, for instance, Dr Barber's Report of the Samalkota Experiment
Station, 1912.

^ Fr. Hansen and J. Hansen, Tidsskriftfor Landbrugets Planteavl, 1913,
XX. 345.

168 Fertilisers [pt.iii

solid and liquid excretions from the animals together with
the litter. It is the oldest and the commonest of all the
fertilisers : indeed in the "sixties " and "seventies" beasts
were kept on the farm solely for the value of the manure
they made, and the practice still persists to some extent.

About half of the bulky food supplied to the animal
(hay, straw, etc.) and nearly all the concentrated food
(corn, cake, etc.) can be broken down by the digestive
fluids in its body; the remainder cannot, and simply
passes out as solid excreta or faeces. The digested por-
tion enters the circulation and is used by the animals,
most of the nitrogen and potash then finds its way into
the urine. The compounds in the urine thus represent
the easily decomposed part of the food, and in the soil
they readily change to ammonia and other useful sub-
stances. On the other hand the solid excreta, which
could not be broken down in the body, prove somewhat
resistent in the soU. Hence the urine is the most valu-
able part of the manure.

The richest manure is therefore that which contains
the most and the richest urine. Now the richness of the
urine clearly depends on the food, for, as we have just
seen, the urine gathers up most of the digested nitrogen;
hence the more digestible nitrogen the food contains, the
richer will be the manure 'produced. Concentrated foods
like cake, which are rich in digestible nitrogen, therefore
improve the dung. But it does not follow that the
richest cake gives the richest manure: richness of cake
depends on the oil present, while richness of the manure
depends on the nitrogen. A linseed cake containing
7 per cent, of oil gives richer manure than a more costly
cake containing 10 per cent., and decorticated cotton
cake gives a richer manure still.

CH. xj Litter 169

But the richness of the urine also depends on the
animal. Fatting animals keep back very little of their
nitrogen — only about 5 per cent. — and pass most of it
out in the urine. Growing animals and milch cows keep
back considerably more, so that the urine is correspond-
ingly poorer. Consequently fatting animals make better
manure than young stock or dairy coivs.

Since the urine contains most of the potash and more
than half of the nitrogen it must on no account be
allowed to waste: sufficient suitable litter must be
added to absorb it all. Straw, peat moss, and bracken
are used for the purpose; they not only absorb the urine
but also enrich the dung because they themselves con-
tain valuable fertilising materials.

Straw is much the commonest form of litter: it
contains a fair amount of nitrogen and of potash,
it has considerable power of absorbing urine and it
encourages a biological fixation of ammonia. Its com-
position varies somewhat (Table IX), but on an average
one ton contains some 18s. worth of fertilising material.

Table IX. Typical analyses of the materials used for
litter. 100 lbs. of each material contain:

Nitrogen Phosphoric acid (P2O5) Potash (KjO)
Oat straw 0-50 0-24 1-00

Wheat straw 0-45 0-24 0-80

Barley straw 0-40 0-18 1-00

Bracken 1-4 0-2 0-1

Peatmoss 0-8 0-1 0-2

Bracken compares very favourably with straw and
should be used whenever opportunity offers, especially
on heavy soils: on sandy soils, however, it suffers from
the drawback — which, however, is not always very im-
portant— that it decomposes more slowly.

170 Fertilisers [pt. hi

Peat moss is not generally nsed on farms as sufficient
straw is usually available, but in city stables it is often
preferred by reason of its higher absorbent power. Peat
moss manure maj'^ be expected to contain more ammonia
than ordinary manure, but on tlie other hand the peat
moss does not itself contribute as much to the manure as
straw, being poorer in potash and phosphoric acid. Fur-
ther it does not so readily decompose and is therefore
less useful on light soils.

The manure as made. Knomng the weight and com-
position of the food and litter and deducting the food
constituents retained by the animal, it is easy to calcu-
late the amount of fertilising materials in any particular
lot of farmyard manure. Experiments by Voelcker,
Wood and the writer show that the calculation does not
come out right, the quantity of nitrogen found in the
manure being usually about 15 per cent, less than was
anticipated. The loss does not take place in the animal :
physiological experiments have shown that the whole
of the nitrogen of the food is excreted in the urine and
faeces: the loss goes on through the action of micro-
organisms wMle the manure is in the stall and before it
is removed. After making this allowance we can find the
total quantity of fertilising material in the heap. The
amount per ton, however, depends on the amount of
water present and tins varies with the different animals ;
sheep and horses giving more concentrated urine and
faeces than cattle and pigs.

In view of the great variability in the quantity and
composition of the litter and of the food it is obvious
that no very definite figures can be given for the com-
position of farmyard manure. Numerous analj^ses have
been made; a few are given in Table X.

CH. x] Storage of Farmyard Mmmve 171

Changes on storing. Dung cannot generally be used
directly it is made but often has to be kept for a period
and applied to the land when convenient. Bacteria,
moulds, etc. cause considerable decomposition during
storage and much heat is evolved. Relatively dry
manure, e.g., horse dung, rises considerably in tempera-
ture; wetter manure like cow dung does not because of
the great amount of heat needed to warm up all the
water present and because much water means little air.
This production of heat involves the combustion of
material in the heap so that there is a corresponding
loss of dry matter. The loss of nitrogen may be con-
siderable and is of course additional to the loss of 15 per
cent. incmTed during the making of the manure.

The changes that take place are very complex : they
are under investigation at Rothamsted by the bacteri-
ologist and the Rupert Guinness chemist. Two groups
of constituents are known to break down; the cellulose
and other carbohydrates in the straw, and the nitrogen
compounds in the straw, urine and faeces. The decom-
position of some of the carbohydrates of the straw is
desirable because they encourage the removal of nitrates
from the soil by micro-organisms, an action which would
be distinctly harmful if it went on to any extent, and
which in fact has caused bad effects when straw has been
applied to soil in sprmg. The necessary decomposition
is brought about in the soil if sufficient time elapses
between the addition of the straw and the sowing of the
seed. This effect of undecomposed straw may be one
reason for the advantage of autumn application of farm-
yard manure over spring application (p. 185).

The breaking down of the complex nitrogen com-
pounds is necessary to provide ammonia and nitrates

172

Fertilisers

[PT. Ill

i

5si

o

O

o

X
pa

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ff

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r^

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C3

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£

2 0)

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-H o -^ CO CO

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O T*< 00 (M O

m r^ t^

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CH. x] Composition of Farmyard Manure

173

a

o
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09
(S

-o

15

o

S-i

a
Q

0-562

0-358
0-381
0-520

0-436

i

o

w

C^ O O — t- CO
(N O O C- CO CO 1
t^ -* l^ CI C-2 O 1

6 6 6 6 6 6

0-535

0-180

0-210
0-266
0-100

CO
Oi

6

CO O O CO CO 00

■<* CO ^ o o; o 1

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6 6 6 6 66

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cq

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t> r-H CO 1-^ ^^ O 1

lO CO CO O ■* CO 1

■^ 'i* t^ 6 TtH lO
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C- t;- -^H C-. ff> 1

CO CO 6 6 6 1

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CO ^ CO »0 CO 00
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Rothamsted 1914

1915-16

Kilmarnock

W. of Scotland dairy farms ...

Wooster, Ohio

Lauchstadt

>

<3

Rothamsted 1914

London (stable manure)
Army manure heaps 1916
Kilmarnock (straw htter)
„ (moss htter)

Wooster, Ohio

Lauchstadt

Average

CO

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174 Fertilisers [pt. iii

for plant nutrition. Complex compounds such as pep-
tone are of little use to the plant even when they are
soluble in water; only the simpler compounds are of
nutritive value. The decomposition in the manure heap
is brought about by micro-organisms, and seems to be
similar in its earlier stages to the hvdrolvsis effected in
the laboratory by acids, giving first aminoacid and
then ammonia. Subsequent events depend on the con-
ditions in the heap. Under anaerobic conditions {i.e. in
absence of air) there seems to be little further change.
Under the mixed conditions of aeration which obtain in
actual heaps there is a loss of nitrogen, which, however,
does not take place under strictly aerobic or strictly
anaerobic conditions. If the heap becomes dry moulds
develop and assimilate some of the ammonia produced,
building it up into forms not available to the plant.
The changes may be summarised as follows:
Under aerobic conditions, i.e. when air is admitted,
some of the carbohydrates of the straw decompose : this
change is advantageous if the manure is to be applied in
the spring, because otherwise there is a loss of soil
nitrates. Some of the nitrogen compounds are decom-
posed, giving rise to ammonia: this also is a useful
change. If the conditions are not wholly aerobic (and
they never are, except in laboratory experiments) there
is always a loss of nitrogen which counteracts the ad-
vantages of the preceding changes. If the heap becomes
too dry moulds develop and take up some of the
ammonia.

Under anaerobic conditions, i.e. when air is excluded,
the straw suffers less change, but the complex nitrogen
compounds break down especially at a temperature of
about 26° C. There is no evolution of gaseous nitrogen.

CH. x] Losses from Manure Heaps 175

These changes so far as they go seem to be entirely
beneficial and involve no loss, but rather a gain, in
value.

Further changes arise when the heap is exposed to the
action of the weather. The rain soaking in encourages
reactions that cause evolution of nitrogen : thus it brings
about considerable loss. Some of the soluble substances
are washed out forming a black liquid which, while it
contains part of the fertilising substances, by no means
represents the whole of the loss sustained bj' the
heap.

Thus the changes are greatest in heaps to which air is
admitted : they are least when air is excluded. The losses
vary in the same way. They are least when air is ex-
cluded and the heap is sheltered from the ram, i.e. in
anaerobic conditions, in a compact heap stored under
cover, or, what comes to the same thing, in manure
made in a box and kept under the animal. They be-
come greatest — amounting to 40 per cent, or more —
when the manure is made in open yards and then loosely
packed into heaps and exposed to rain in the open. In
the Rothamsted experiments the losses on storage for
three months were :

Compact heap under cover: 4 per cent, of nitrogen.
Loose heap under cover : 7 ,, .,

Heap exposed to open : 33 „ „

The loss fell mainly on the ammonia and amides, i.e.,
on the easily available nitrogen. (Fig. 34.)

On this basis a 100 ton heap of manure valued at lOs,
a ton would have lost over £16 worth of material in three
months' exposure to the weather.

Formerly it was supposed that the loss of nitrogen
took place mainly as ammonia, and farmers were ad-

176

Fertilisers

[PT. Ill

vised to mix superphosphate, gypsum, or soil with the
heap as "fixers," but recent work is against this view
and direct experiment has shown the futihty of these
precautions^. Shelter and coinpacting seem the best
methods of reducing the loss.

Nitrogen

as NH.,

as Amide

as other

Nitrogen

Compounds

19

IS

10
II

7^

9

to
7'

]L

^

9
6Z

At start

Kept compact
and covered

Kept loose
and covered

Kept loose
and exposed

Fig. 34. Changes in nitrogen compounds in farmyard manure (cow
manure) kept for three months,. January 23 to April 30, 1914.

The following are general rules for the more efficient
conservation of the fertilising constituents of farmyard
manure :

I. Manuremadefrom fatting beasts. If this is made in
covered yards it should be left under the beasts until it

^ In the Ohio experiments, however, gypsum proved effective.

CH. x] Liquid Manure 177

is wanted. Defective roofing and spouting should be
made good so far as possible to avoid washing by rain.
If made in open yards the manure should as soon as
convenient be hauled out and tightly clamped.

The clamp should be so placed that it is not unduly
exposed to rain. Shelter should be provided in the form
of a layer of earth, thatched hurdles, corrugated iron
sheets, etc. If any black liquid is running away it is a sign
tliat shelter is insufficient and that wastage is going on. It
is not sufficient to collect the liquid, though this should be
done ; steps should be taken to provide more shelter also.
The clamp should not be disturbed until it is wanted.

If it is possible to avoid maldng the clamp by putting
the manure straight on to the land and ploughing it in,
so much the better; especially in the regions south of
the Humber. As far as possible summer storage of
manure should be avoided.

II. Manure 7iiade from dairy cattle. This has usually
to be thrown out daily. It should be well protected from
rain. The worst plan is that seen in some of the northern
dales where the manure is thrown out of a hole in the
wall and left exposed to weather, with the result that
streams of black liquid flow away. A much better plan
is to cart the manure to a dungstead as is done in
Cheshire and other parts of the country.

Liquid 7nanure. Special care should be taken of the
liquid manure draining from the cow sheds. This should
be run into a tank^ and applied when convenient to the
land. It may go on to grassland at almost any time, and
to arable land after the autumn and before the middle or
end of May. It is specialJj^ rich in nitrogen and potash as
shown in Table XL

1 For details of tank see Leaflet F P. 449/01, Board of Agriculture.
E. s. 12

1/8

Fertilisers [pt. hi

Table XI. Comj^osition of liquid manure

Percentage composition 100 gallons contain in lbs.

Nitrogen
(N)

Phosphate

Potash
(KjO)

Nitrogen
(N)

Phosphate ' Potash
iPpi) , (K,0)

English samples :

Kent

Surrey
Scotch samples 1

•18
•23

•20

•017

•03

•03

•40

•46

18^2
23 0
20-5

11 401

30 460

1
1

The general experience of farmers and direct field
experiments in Scotland and Ireland have demonstrated
its fertilising value^.

Effect of the manure. Practical men distinguish be-
tween "long" manure which has suffered only little
decomposition, and retains its straw in the original long
state, and "short" manure, where decomposition has
proceeded so far that much of the straw has disinte-
grated to form a black buttery mass. The "short"
manure is often richer in composition than the "long"
manure, but it is more costly to produce because as
much as two tons of fresh manure may be needed to
make a ton of short manure, while the same quantity
of material would yield 35 cwt. or more of long manure.
For this reason long manure is most in favour on the
farm, where costs have to be considered, wliile short
manure is preferred in the garden.

Long manure acts best when it can be applied in
autumn. The undecomposed straw is of special advan-
tage on a heavy soil since the straw helps to keep the

^ Hendrick, N. of Scotland Coll. of Agric. Bull. No. 19, 1915; Journ.
Irish Dept. of Agric. xiii. 251. For an illustration of the use of hquid
manure on the large scale see the account of Miss Coat's fai'm in Country
Jjife.

CH. x] Cake-fed DniU) 179

soil open and to facilitate drainage and the action of
winter frost. The harmful effect on the soil nitrates
alreadj^ noted (p. 171) is not produced to any notable
extent during this season of the year; the straw has had
time to become disintegrated, and its reactive con-
stituents to decompose, before the spring comes round.

On the other hand spring applications of long manure
suffer from certain disadvantages; there is the possi-
bility of loss of nitrate and on light land or in dry dis-
tricts the undecomposed straw may open up the soil too
much and cause loss of water. These disadvantages do
not operate in wet districts.

Short manure can be used at almost any time of the
year and is therefore necessary for many garden pur
poses.

The distinction between cake-fed dung and ordinary
dung produced by store cattle has already been dis-
cussed. Cake-fed dimg, as shown on p. 172, is richer in
nitrogen than dimg produced on hay and roots only,
and is even better than the figures indicate because the
extra nitrogen is largely in the form of ammonia and
amides produced from the liquid excreta. These com-
pounds readily change to nitrates in the soil and so give
rise to increased crops. Some of the data obtained at
Rothamsted are given in Table XII.

On the heavy soil at Rothamsted and the similar soil
at Garforth the advantage of the cake feeding was not
seen after the second year ; experiments on other types
of soil would be needed to discover how far this effect is
general.

The two most striking physical effects of farmyard
manure on the soil are the improvement in tilth already
referred to, and the improvement in the water-holding

12—2

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CH. XJ

Effect on Soil Moisture

181

capacity. Fig. 35 gives curves showing the percentage
of water in the dunged plot and in the adjacent unma-
nured plot of the Broadbalk wheat field during 1913-14:
it will be seen that the former is invariably the moister
even in the very dry June. Indeed so great is the water-
holding capacity of the soil that the rain-water does not
distribute itself uniformly in the soil but remains in the
top few inches and rarely gets down to the drains in

30
25

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June. July.
1913

Aug. Sep. Oct. Nov. Dec.

Jan.

Feb. Mar. Apr May.

Fig. 35. Curves showing effect of farmyard manure on water
content of soils. (Broadbalk field, Rothamsted.)

sufficient quantity to cause them to run. The unmanured
soil, on the other hand, is easily permeable to water,
becomes wet throughout its depth soon after rain has
fallen, and readily transmits water to the drains. The
numbers of days when the drains ran are as follows :

1903

1904 1905 \ 1906

1907

1908

1909

1910

1911 1912

1913

1914

.-Vverage of
12 years

Dunged plot
Unmanured
plot

2
27

1
3 None' 1

20 11 ! 14

None None
10 9

1
10

None
20

None None
20 32

None
39

2

20

0-7
17

182

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CH. X]

Lasting Ejfect on Fertility

18a

On the mangold fields these physical effects on tilth
and moisture supply considerably help the young plant
in a dry season. (Fig. 36.)

The effect of farmyard manure in building up fer-
tility of the soil is strikingly shown on one of the barley
plots at Rothamsted. This received farmyard manure
annually for 20 years from 1852 to 1871, but nothing

60

50

e 40

o

e«

ID

"^30

I— (

m 20

10

0

^^

s
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^ ^

■

\

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"* ^

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7-2

7-1

1-0

1852-1861 1862-1871 1872-1881 1882-1891 1892-1901 1902-1911

Fig. 37. Yield of barley in successive ten year periods, 1852-1911.
Plot 1-0. Unmanured Plot. Plot 7-2. Farmyard Manure.

Plot 7-1. Farmyard Manure 1852-71; unmanured 1872-1911.

since. Alongside is a plot that has received nothing
during the whole period. The effect of the farmyard
manure went on increasing during the first 13 years; it
then increased no more, but kept at its high level. In
1872 the farmyard manure was discontinued. The yield
has gradually fallen, but even after 46 years it is still
well above the level of the unmanured plot (Fig. 37).

184 Fertilisei'S [pt. hi

In farm practice the good effect of farmyard manure
is intensified by another interesting property. It has a
remarkable effect on increasing the growth of clover.
This was well shown on the Little Hoosfield Plots in
1917 and 1918. Those which had received farmyard
manure in the preceding year, and even two or three
years before, gave a much better clover crop than those
which had only received artificials, and this was followed
by a better wheat crop.

Dung for Artificials No manure

previous for previous for previous

crop crop crop

Clover hay: cwts. per acre, 1917 65-6 41-9 41-1

Wheat: bush, per acre, 1918 44-0 37-1 36-8

When clover is good it makes the next crop good also
because it enriches the soil in organic matter and in
nitrogen taken from the atmosphere. Thus, farm^^ard
manure not only itself adds to the organic matter of the
soil, but also ensures a further supply through the
agency of the clover crop.

Farmyard manure considerably influences the micro-
scopic population of the soil, causing the numbers of
bacteria and other organisms to increase and bringing
into prominence certain changes that are not con-
spicuous in ordinary soils.

On the heavily dunged Broadbalk plot (14 tons
annually) about 30 to 50 per cent, of the nitrogen in
the dung is absorbed by the crop or washed out, and
about 20 per cent, accumulates in the soil, but the re-
mainder cannot be accounted for, and the simplest
explanation is that it is lost as gaseous nitrogen.
Equally serious losses seem to occur wherever dung is
used in heavy dressings, e.g.. in market gardening, in
certain glasshouse work, and in intensive mangold grow-

CH. xj Time of Application 185

ing. On the other hand there seems to be less loss where
the clung is only applied once in four years as in ordinary
farming, and where proper rotations and well-balanced
manurial schemes are adopted. The cause of the loss is
being investigated at Rothamsted.

The use of farmyard mariure. As a fertiliser farmyard
manure is well supplied with nitrogen and potash, but
deficient in phosphates, and the best results are obtained
when the necessary artificial manures are applied some-
where in the rotation. The dung is usually put on to the
roots, especially to the mangolds and potatoes, some
also can go on the young seeds and some to the meadow
land. The time of application depends on the climate,
the crop, and the labour available. So far as labour is
concerned it is an advantage to apply the manure in
autumn or winter and get it worked in ready for the
spring, and this can be done in districts with an annual
rainfall of 30 inches or less. In wetter districts, however,
with a rainfall of 35 inches or more, better results have
been obtained by spring dressings. Cases have arisen
where autumn dressings on seeds mixtures have kept
the land so wet that young clover plants have suffered.
Berry has shown in the west of Scotland that spring
dressings gave increases of 50 to 60 per cent, in the
potato and turnip crops while autumn dressings only
gave 25 per cent, increase over the control plots ^.

Farmyard manure sometimes contains many weed
seeds and the old practice was to kill them by throwing
the heap up loosely and allowing it to become hot. But
the modern threshing machine is considerably more
efficient than the older form, and the weed seeds are
more completely removed with the cavings; so long as

^ West of Scotland Agricultural Bulletin, No. 65, 1914.

186 Fertilisers [pt. hi

these are not thrown on to the manure heap there is
little if any need to take special precautions against
weeds. On a clean farm even the cavings can be used
with advantage. Purchased town manure should, as
far as possible, be clamped in autumn and left as long
as convenient to kill weeds.

Finger and toe may be carried in manure if animals
are fed on diseased roots.

Unexhausted values. Farmvard manure is in rather a
different category from the artificial nitrogenous fer-
tilisers in that its effects are not confined to the season
of application but persist over several years. So long
as a farmer continues in possession of the land he may
hope to gain the benefit, but if he gives it up before the
effects have come to an end he is entitled to compensa-
tion for the unexliausted value of the manure. The first
tables for the guidance of valuers were drawn up by
Lawes and Gilbert in 1870; they have been periodically
revised and were reissued in 1914^ by Voelcker and
Hall, who recommend: (a) compensation should be pay-
able in respect of half the nitrogen and three-quarters
of the potash and phosphoric acid contained in the food,
it being supposed that the remainder is lost : this amount
to be paid in full where the manure has been applied to
the land but no crop grown; (6) only one half the above
amount is to be paid after the growth of one crop, and
nothing is to be paid after the growth of two or more
crops; (c) where, however, the food is fed on the land
and not made into manure a higher scale of compensa-
tion should be payable, and credit be given for 70 per

1 Journ. Boy. Agric. Soc, 1914, iaxiv. 104. For other papers on the
subject see Leeds Bull. Nos. 43, 51 and 94 (Root and Meadow land: Pig
manure) ; Cockle Park Bull. No. 4 ; Gilchrist, Trans. Surveyors Instil., 1916.

CH. x] Composts 187

cent, of the nitrogen instead of the 50 per cent, in (a).
This higher rate, however, is only appUcable before a
crop is grown because the extra benefit is attributed to
the ammonia formed from the urine. Their values are
given in Table XIII. The weakness of the method as
generally practised is that the nitrogen of farmyard
manure is not always good for grass land^ and yet the
incoming tenant is expected to pay for it.

Composts. A compost is a heap of mixed vegetable
and animal matter put up so that it can decompose and
form useful organic manure. The art of making com-
posts was well known to agriculturists during the 'fifties
and 'sixties of the past century, and farmers and
gardeners made great use of them before large quantities
of artificial fertilisers were available. Indeed, in the
Gardeners' Chronicle for 1845, Mr Errington describes
no fewer than 20 different composts for garden pur-
poses, and explains their uses. He attributes some of
the most marked of the then recent advances in horti-
culture to a better understanding of the use of com-
posts.

Mr Hannam of Kirk Deighton, Wetherby, writing in
Morton's Cyclopaedia of Agriculture in 1855, describes
the best method known to him of making composts on
the farm. He describes three kinds, Farmyard Manure
composts, Lime composts and Earth composts. The
Farmyard Manure composts were made by mixing sods,
turf, leaves, heath, moss, rushes, weeds, clippings, etc.
(but not animal refuse), with farmyard manure in
alternate layers each about 1 ft. in thickness, and
covering the whole with a coating of earth. After the
mass had undergone considerable decomposition it was
^ See e.g. Hanging Leaves field at Cockle Park.

188 Table XIII. Showing the compositio)

, raanurial and compensatio)

Valuation

per ton a

Nitrogen

Phosphoric

Acid

Per

Value

Half of

Per

Value

Three-

No. Foods

cent.

at 15s.

value to

cent.

at 35.

quarters

of value

to manur

in food

per unit

manure

in food

per unit

s. d.

5.

d.

.9. d.

s. d.

1. Decorticated cotton cake

6-90

103 6

51

9

3-10

9 4

7 0

2. Undecortd. cotton cake (Egyptian)

3-54

53 2

26

7

2-00

6 0

4 6

3. Undecortd. cotton cake (Bombay)

3-10

46 6

23

3

2-50

7 6

5 7

4. Linseed cake

4-75

71 4

35

8

2-00

6 0

4 6

6. Linseed

3-60

54 0

27

0

1-54

4 7

3 5

6. Soya-bean cake

6-85

102 8

51

4

1-30

3 11

2 11

7. Palm-nut cake

2-50

37 6

18

9

1-20

3 7

2 8

8. Coco-nut cake

3-40

51 0

25

6

1-40

4 2

3 1

9. Earth-nut cake

7-62

114 4

57

2

2-00

6 0

4 6

10. Rape cake

4-90

73 6

36

9

2-50

7 6

5 8

IL Beans

4-00

60 0

30

0

1-10

3 4

2 6

12. Peas

3-60

54 0

27

0

0-85

2 7

1 11

13. Wheat

1-80

26 10

13

5

0-85

2 7

2 0

14. Barley

1-65

24 10

12

5

0-75

2 3

1 8

15. Oats

2-00

30 0

15

0

0-60

1 10

1 5

16. Maize

1-70

25 6

12

9

0-60

1 9

1 4

17. Rice meal ...

1-90

28 8

14

4

0-60

1 9

1 4

18. Locust beans

1-20

18 0

9

0

0-80

2 5

1 10

19. Malt

1-82

27 4

13

8

0-80

2 5

1 10

20. Malt culms

3-90

58 6

29

3

2-00

6 0

4 6

21. Bran

2-50

37 6

18

9

3-60

10 10

8 2

22. Brewer's grains (dried)

3-30

49 4

24

8

1-61

4 10

3 8

23. Brewer's grains (wet)

0-81

12 4

6

2

0-42

1 3

0 11

24. Clover hay

2-40

36 0

18

0

0-57

1 9

1 4

25. Meadow liay

1-50

22 6

11

3

0-40

1 2

0 11

26. Wheat straw

0-45

6 8

3

4

0-24

0 9

0 7

27. Barley straw

0-40

6 0

3

0

0-18

0 6

0 4

28. Oat straw

0-50

7 6

3

<)

0-24

0 9

0 7

29. Mangolds

0-22

3 4

1

8

007

0 3

0 2

30. Swedes

0-25

3 10

1

11

006

0 2

0 1

31. Turnips

018

2 8

1

4

0-05

0 2

0 I

values

of j'eedmg stuffs ( Voelcker and HalVs Tables, 1914)

189

manure

Compensation value for each ton of the food consumed

Potash

Food made

s into dung

Food consumed on land

(1)

(2)

(3)

(4)

Per

CGIlt.

Value
at 4t5.

Three-

Before one

After one

Before one

After one

quarters

crop has

crop has

crop has

crop has

No.

in food

per unit

of value

been grown

been grown

been grown

been grown

to manure

or removed

or removed

or removed

or removed

5. d.

s. d.

s. d.

s. d.

.«. d.

s. d.

2-00

8 0

6 0

64 9

32 4

85 6

32 4

1

2-00

8 0

6 0

37 1

18 6

47 9

18 6

2

1-61

6 5

4 10

33 8

16 10

43 0

16 10

3

1-40

5 7

4 2

44 4

22 2

58 10

22 2

4

1-37

5 6

4 2

34 7

17 3

45 4

17 3

5

2-20

8 10

6 7

60 10

30 5

81 6

30 5

6

0-50

2 0

1 6

22 11

11 5

30 6

11 5

7

2-00

8 0

6 0

34 7

17 3

44 9

17 3

8

1-50

6 0

4 6

66 2

33 1

89 1

33 1

9

1-50

6 0

4 6

46 11

23 5

61 8

23 5

10

1-30

5 2

3 10

36 4

18 2

48 4

18 2

11

0-96

3 10

2 10

31 9

15 10

42 6

15 10

12

0-53

2 1

1 7

17 0

8 6

22 5

8 6

13

0-55

2 2

1 7

15 8

7 10

20 8

7 10

14

0-50

2 0

1 6

17 11

9 0

23 11

9 0

15

0-37

1 6

1 1

15 2

7 7

20 4

7 7

16

0-37

1 6

1 1

16 9

8 4

22 6

8 4

17

0-80

3 2

2 4

13 2

6 7

16 9

6 7

18

0-60

2 5

1 10

17 4

8 8

22 9

8 8

19

2-00

8 0

6 0

39 9

19 10

51 6

19 10

20

1-45

5 9

4 4

31 3

15 7

38 10

15 7

21

0-20

0 10

0 8

29 0

14 6

38 11

14 6

22

0-05

0 2

0 1

7 2

3 7

9 9

3 7

23

1-50

6 0

4 6

23 10

11 11

31 0

11 11

24

1-60

6 5

4 8

16 10

8 5

21 4

8 5

25

0-80

3 2

2 4

6 3

3 1

7 7

3 1

26

1-00

4 0

3 0

6 4

3 2

7 6

3 2

27

1-00

4 0

3 0

7 4

3 8

8 11

3 8

28

0-40

1 7

1 2

3 0

1 6

3 8

1 6

29

0-22

0 11

0 8

2 8

1 4

3 7

1 4

30

0-30

1 2

0 11

2 4

1 2

2 10

1 2

31

1^0 Fertilisers [pt. iii, ch. x

turned and roughly mixed, and a covering of ashes,
charcoal or earth again spread over it. Liquid manure
was sometimes added.

Earth composts were made by mixing soil with animal
matter, waste fish, blubber, woolwaste, shoddy, etc., and
treating the heap as before. The resulting fine earth was
drilled with seed so that the young plant started well in
the artificial soil. The results obtained from a well-made
compost were said to be as good as from farmj^ard
maniu-e.

Lime composts were made by mixing lime with peat,
sawdust, bark, roots of couch grass, hedge clippings,
ditch scourings, road scrapings, weeds from fallows,
sods, etc., the mixture being as uniform as possible. The
heap was turned two or three times before use, and was
ready in two or three months.

Lime composts are still used in Cumberland for pas-
ture land with good results. Road and yard scrapings,
contents of cess pits, ditch cleansings, etc., are mixed
with about one-eighth their bulk of burnt lime.

CHAPTER XI

OTHER ORGANIC MANURES

(A) Animal Origin
Gtiano

Guano consists of the droppings of pelicans and other
sea birds mixed with feathers, corpses of dead birds,
remains of food, etc. It first came into this coimtry
from Peru in 1840 and rapidly achieved a high reputa-
tion. Other supplies have since been drawn from the
numerous islands of the South Pacific. Deposits also
occur on some of the islands off the coast of South
Africa, especially Ichaboe, but these are retained for
local consumption by the Union Government and are
not generally shipped to Europe.

The composition and character of the guano depend
on the conditions under which it has accumulated: in
rainless areas it rapidly dries and remains undecom-
posed : in wet areas it suffers considerable decomposition
and loses much of its nitrogen and organic matter, be-
coming more phosphatic. Thus two grades of guano are
available: the nitrogenous, obtained in rainless districts,
and the phosphatic, from moister regions.

The chief European supply of nitrogenous guano is
from the rainless islands off the coast of Chili and Peru
(lat. 7° to 20° S.). These are uninhabited and practically
unvisited except at long intervals for the purpose of
clearing the accumulations. The birds are carefully pre-
served and care is taken by the Government and the

192

Fertilisers

[PT. Ill

large firms controlling the industry to ensure continuity
of supplies for the future. The Ichaboe guano used in
South Africa is collected annually after the breeding
season is over: it is thus the freshest on the market. It
usually contains less phosphate and more sand than the
Peruvian guano of corresponding grade.

The phosphatic guanos are obtainable from a wider
area and show larger proportions of phosphates and
rock material by reason of the removal of the organic
matter.

The composition of these guanos is as follows:

Nitrogen

PaOg

Equivalent
to tricalcic

Potash
K2O

Moisture
and

Sand

phosphate

organic
matter

Nitrogenous

-

High grade

Peruvian

10-14

9-11

20-24

2-4

60-70

7-12

Ordinary „

5-8

14-18

30-40

2-4

40-50

9-25

Ichaboe

8

9-14

20-30

2

.50-60

15-25

Pliosphatic

2-5-30

18-32

40-70

2-6

22-25

4-6

The high grade Peruvian guanos are used in horti-
culture, the ordinary grades in market gardens and
occasionally for potatoes. It is quick acting and its
effect at Rothamsted only lasts for one season (Table
XIV) ; it is somewhat superior to rape cake and shoddy,
but not to sulphate of ammonia^. The phosphatic
guanos are used both in market gardens and on farms.
Other grades are treated Avith sulphuric acid to
decompose the phosphates and form "dissolved guano,"
which is used in intensive cultivation here and on sugar
plantations in the West Indies.

1 Rothumsled Annnal Rpl., 1917; Leeds Bull. No. 3. 1898.

CH. XlJ

Fish Gua7io

193

Table XIV. Effect of Peruvian guano on yield of crops.
Rothamsted, Little Hoosfield. Total iwoduce per acre
{unmanured =100)

Barley
1909

Wheat
1910

Man-
golds
1911

Wheat
1912

Unmanured

Year of application

1st year after application

2nd

3rd

100
152

80
89
90

100
124

77
64

87

100
120

94

97
89

100
107

98
84
90

Swedes
1913

Barley
1914

Man-
golds
1915

Wheat
1916

Mean
1904-16

Unmanured

Year of application

1st year after application

2nd

3rd

100
164

115
103
113

100
180

92
70
81

100
125

106

106

73

100
139

86
90
95

100
142

95
91
89

Manufactured manures. — Fish guano. Eish guano or
fish meal is obtained from fish which for any reason
cannot be sold as food. The oil is first extracted by-
heat and pressure and the residue is then finely ground.
It usually contains about 8 to 10 per cent, of nitrogen,
about 1 per cent, of K2O, and 4|^ to 9 per cent, of PgOg,
equivalent to 10 to 20 per cent, of tricalcic phosphate^;
sometimes, however, more bone is present. It is a verV
useful manure for hops and in gardens, and has given
good results when applied at the rate of 4 lbs. per rod

^ A large number of samples from the North Shields district analysed
by Collins had the following mean composition:

N 8-0±0-2 %; P2O5 5-9±0-8 %; K^O M±0-3 %.
R. s. 13

194

Fertilisers

[PT. Ill

to lawns on thin dry soils: it is also useful in farm
practice. Care should be taken that it is groiuid suffici-
ently to reduce the bone to a fine state. It must be got
into the land quickly or it may be taken by birds.

Meat guano or meat meal, greaves

This is prepared from tankage from the Argentine,
and some also from waste meat, condemned meat, refuse
from slaughter houses, etc. It is first heated by steam
to extract some of the fat and then subjected to pressure
to remove as much more as possible — this process being
adopted because of the high commercial value of fat for
the soap and candle industries. The resulting cake is
then broken up, dried, separated by shaking from
foreign matter such as iron, glass, and is finely ground.
Some of the fibrous material which still remains can
only be disintegrated after treatment with sulphuric
acid.

Some bone is always present, and definite quantities
are added in certain cases to bring the composition to
a uniform grade. The composition of various grades is
as follows :

Nitrogen '

P2O5

Equivalent to
Tricalcic phosphate

Pure flesh, dry and fat
free

High grade meat guano

Phosphatic meat guano
(bone added)

Pure bone

16-7
8-9

5-6
5

4-6-7

11-5-16
22

10-15

25-35

48

Greaves is the waste material sent out by soap boilers
and others ; it is of substantially the same nature as meat
guano, but not being a definitely manufactured manure

CH. XI] Oil Cakes 19b

it is liable to variations in composition and physical con-
dition: it should only be bought after analysis and at
prices less per unit than meat or fish guano.

Dried blood. This usually contains about ] 2 per cent,
of nitrogen though occasional samples rise nearly to
15 per cent, and it decomposes so rapidly that it com-
mands a specially high price, and indeed is usually too
costly — about £12 per ton before the war — for ordinary
purposes. It is, however, used in high class horticultural
work, e.g., for roses, carnations, vines, etc., and much
of it is bought for America and for the better grade of
mixed and patent fertilisers.

Hoofs and horns. Good samples of these contain 12 to
14 per cent, of nitrogen. When finely divided they are
very effective for glasshouse work, and competition for
the supply has sent up prices considerably ; hoofs are
supposed to be better than horns. Another grade
admixed with bone is also obtainable containing about
10 per cent, of nitrogen and 20-25 per cent, of phosphate.
"Dust to |-inch" is a favourite grist; coarser samples
are of little use, and the rough material called scutch,
sometimes offered for farm use and consisting of hair,
hoof and bone, should only be applied after it has been
well broken up,

(B) Vegetable Origin
Oil cakes

The large demand for oils and fats has created an
enormous industry in pressing out oil from oil seeds.
In some cases — e.g., linseed and cotton — the residues
have considerable value as cattle food: in other cases
they are unsuitable for this purpose and are then offered
as manure. The best known in this country is rape cake,

13—2

196

Fertilisers

[PT. Ill

which usually contains about 5 per cent, of nitrogen,
2 per cent, of P2O5 {i.e., 4 per cent, of "phosphate")
and 1 per cent, of potash.

Rape cake has long been used as a manure with good
results^ in this country and in India, and numerous ex-
periments at Rothamsted have proved its value both
on cereals and on roots (Table XV). There is nothing
to show, however, that it is worth a higher unit price
than the various guanos, and yet higher prices are not
uncommonly asked.

Table XV. Effect of ra^ie cake on yields of barley
and mangolds, Rothamsted

Barley

Mangolds

Plot

Average yield

for 60 yrs.

(1852-1911)

Plot

Average vield
for 34 vVs.*
(1876-1912)

Grain,

Straw,

tons

bushels

cwts.

per acre

Unmanured

1-0

12-7

8-4

8-0

3-7

Complete artificial

manures

4-AA

42-7

27-3

4-A

14-8

Farmyard manure

(14 tons)

7-2

47-1

29-6

1-0-

18-9

Rape cake (9 cwt.)

Ici

38-3

22-1

6-c3

19-3

^ Rape cake alone: the addition of potash and phosphates has very
little further effect.

2 Dung + potash and phosphates: this yield is, however, almost the
same as with dung alone.

8 Rape cake + potash and phosphates, these being specially needed for
mangolds.

* 18S5, 1901, and 1908 omitted.

The effect only lasts for one year at Rothamsted and
no evidence has been obtained of any residual effect
(Table XVI).

* An interesting old account is given by Hannam in Journ. Roy. Agric.
Soc, 1848, IV. 177.

CH. Xl]

Seaweed

197

Table XVI. Immediate and subsequent effects of rape
cake. Rothamsted, Little Hoosfield. Total produce
per acre {unmanured = 100)

Barley
1909

Wheat
1910

Man-
golds
1911

Wheat
1912

Unmanured

Year of apphcation

1st year after application

2nd

3rd

100
125

90

112

93

100
125

81

78
90

100
114

91

92

84

100
131

119
105
106

Swedes
1913

Barley
1914

Man-
golds
1915

Wheat
1916

Mean
1904-16

Unmanured

Year of application

1st year after application

2nd

3rd

100

78

115
100

96

100
181

153
101
118

100
185

159
156
113

100
143

118
132
133

100
136

110
106
102

Castor meal is also used to some extent. Oil cakes
residues play a very important part in Indian and
Japanese agriculture and not infrequently prove better
and cheaper than artificial manures (p. 196).

Seaweed
Seaweed is one of the oldest manures known and has
been in use since remote ages in the coastal districts of
Great Britain. It is so important in Jersey that the
dates for cutting are annually fixed and announced by
the Court, while the collection, drying and stacking
afford regular summer occupation to some of the poorer

198 Fertilisers [pt. hi

people : in Scotland also the right to collect it sometimes
forms part of the covenant with the landlord. Seaweed
contains about the same amount of nitrogen as ordinary
farm crops, and a considerably higher percentage of
potash than these or the Zostera and other plants often
collected with it. The different weeds vary, the long
broad leaf -like Laminaria being richer than Fucus, the
common bladder-wrack of the rocks. Further the weed
cut or thrown up earlj'^ in the year is richer than that
obtained later in summer or autumn. The average com-
position of wet weed is usualW^:

Water Organic matter Nitrogen Potash (KoO) PjOj

70-80 13-25 0-3-0-5 0-8-1 -8 0-02-017

It is thus YQvy similar to farmyard manure except
that it contains less phosphoric acid. On drjdng, how-
ever, a very rich manure is obtained which ought to be
utilised to a greater extent than is done at present.

It is largely used for potatoes in Jersey and in Scot-
land, the dressings being from 25-30 tons in Ayrshire
and up to 45 tons in Jersey: some artificials are also
applied. In Thanet 10-15 tons per acre is applied to
lucerne and to market garden crops.

Definite manurial trials with fresh seaweed as hauled
up in farm carts have been made in Scotland by Hend-
rick^ and in Ireland by the officers of the Department^.
The general result is that fresh seaweed is not much
inferior to dung, while there can be little doubt that
dried weed powdered up would make an admirable
concentrated fertiliser.

1 See Joiirn. Board of Agric, 1910, xvii. p. 458 and LeaOet 254, fur
fuller details on the composition and use of seaweed as manure.

2 Trans. Highland and Agric. Soc, 1898, p. 118.

3 Jouni. of the Dept. of Agric. and Tech. Instruction. Jan. I!tl4.

CH. Xl]

Shoddy

199

(C) Waste Products from Manufactories
AND Towns

Slioddy

Shoddy is the waste material turned out from the
Yorkshire mills which tear up old cloth and woollen
rags and make them into new cloth ; it consists of the
fragments that are too small to be picked up by the
machine. Three groups may be distinguished. The high
grade contains 12 to 14 per cent, of nitrogen, it is pure
and free from cotton or dirt, but is largely purchased for
the manufacture of compound or patent manures.

Table XVII. Effect of shoddy on crops. Rothanisted,
Little Hoosfield. Total produce per acre (un-
manured = 100)

Barley
1909

Wheat
1910

Man-
golds
1911

Wheat
1912

Swedes
1913

Unmanured

Year of appUcation

1st year after apphcation

2nd

3rd

100

118

103
142
116

100
135

93

90

100

100
126

120
99
99

100
117

123
126
108

100
135

119
91
71

Barley
1914

Man-
golds
1915

Wheat
1916

Mean
1904-16

Unmanured

Year of application

1st year after apphcation

2nd

3rd

100
161

99

87

115

100
124

106
93

77

100
106

116
111

78

100
136

121

108
98

200 Fertilisers [pt, hi

The medium grade contains 5 to 8 per cent, of nitrogen
and is considerably admixed with cotton, dirt and some-
times oil: larger supplies are available and it is much
used in hop gardens where it is ploughed in during
winter at the rate of 1-2 tons per acre. At Rothamsted
1 ton per acre has given good results on farm crops, and
the effect of the dressing even persists into the second
and third years (Table XVII).

The lowest grade is sometimes very poor, containing
only about 3 per cent, of nitrogen, and should only be
purchased when it can be had cheaply.

Acidulated or dissolved shoddy is prepared by treat-
ing shoddy with sulphuric acid in such a way that most
of the fibre is destroyed ; it is sometimes used on heavy
soils under the name of "organic meal," and also as a
base in the manufacture of compound fertilisers.

Other waste products'^. From time to time various
nitrogenous or phosphatic substances are available as
manure and can be purchased at fairly cheap rates.
Their value depends on their composition, freedom from
toxic substances, and mechanical condition : they should
therefore only be purchased on analysis. The proper
way of dealing with them would be to submit them to a
preparatory grinding and mixing, but often the supplies
are too small or too irregular to justify the erection of
plant for the purpose.

Hair, calf hair, etc., contains about 10 per cent, of
nitrogen but is very slow to decompose in the soil
especially in its usual long state: it should be only
used when it can be obtained very cheaply and is in
fair mechanical condition.

Feathers containing about 9 per cent, of nitrogen are

* Described in more detail in Board of Agric. Leaflet, No. 175.

CH.xi] Leather Waste 201

used with advantage in hop gardens. The larger quills
are more in demand than the small feathers and they
contain more nitrogen.

Rabbit waste consists of the ears, feet, tail, etc., of the
rabbit, and so far as the supply goes it is distinctly
useful as manure and is improved by properly grinding.

Leather waste. Boot leather waste has at times been
offered to farmers, but it has never been shown to
possess manurial value and should not be purchased,
nor should it enter into the composition of a mixed
manure. Unfortunately finely ground samples contain-
ing some 7 per cent, of nitrogen are periodically offered
for sale at low prices, and there is reason to believe
that they are sometimes used in compound and patent
manures to give a high nitrogen content, and an
undeserved appearance of richness. This is the more
regrettable as leather might probably be made a useful
manure by suitable treatment.

Soft leather scraps obtained from glove factories are in a
different category, and find valuable applicationin market
gardens in the glove districts of Worcestershire : they are
put into the soil with the young sprouts, cabbages, etc., at
the same time of setting out and afford a useful root run.

Dissolved or acidulated leather is prepared by digest-
ing scraps of boot and other leather with sulphuric acid
of the proper strength at a certain temperature, when
the whole mass melts and some at any rate of its
nitrogen compounds become soluble. Until recently it
was exported to America where it was used as a base
for compound fertilisers. French manurial trials have
given fairly satisfactory results^.

I ^ R. Giiillin, Annales Science Agronomique, 1916, xxxni. 337. See
also U.S. Deft, of Agric. Bull. No. 158.

202 Fertiliser's [pt. hi

Soot and flue dusts. Three types of soot and flue dusts
are available, only two of which, however, possess
manurial value.

1. Household soot, which may contain anything
from 2-5 to 11 per cent, of nitrogen (equivalent to 3 to
13 per cent, of ammonia); the lower values are given
by mixed samples from dwelling houses, and the higher
ones from the light fluffy soot, obtainable from sitting-
room or kitchen chimneys ; a usual amount may be put
at about 4 per cent. As soot is purchased by the bushel
it is moie useful to know the quantity of nitrogen per
bushel; this is much less variable than the figures for
the percentage composition, because the rich soot is
very bulky and the poor soot is more dense. Analyses
at Cambridge showed that as a rule 1 bushel of soot
contains 1 lb. of nitrogen (mainly as sulphate of am-
monia) normally worth about Id. (p. 136). It contains
some substance disagreeable to slugs and other pests,
and it improves the physical conditions in the soil
partly by ameliorating the texture and partly by the
warming effect of its black colour. It is applied at the
rate of 20-30 bushels per acre as a spring dressing for
wheat, supplying both the nitrogen and the warmth
that is then needed ; and it is also used for hops in Kent,
quantities being sent for the purpose from Manchester
and other northern cities^.

2. Blast furnace flue dust. This is quite a different sub-
stance from the foregoing, and owes its value not to nitro-
gen but to the potash which has been volatilised from the
coal, ore andflux by theintense heat of the furnace (p. 154).

^ Knccht has extracted a number of interesting compounds from
Manchester soot, including a paraffin C27H5g that is also present in
beeswax. Proc. Manch. Lit. and Phil. Sot., 1905, p. 49.

CH. xij Seivage 203

3. Soot from destructors and boilers, however, is of
very much less value, commonly containing about 0-5
per cent, of nitrogen, and less than 1 per cent, of potash.
On no account should any of these be purchased except
on the recommendation of a disinterested analyst.

Two such samples showed the following percentages :

Nitrogen Potash (KgO)

1. 0-5 —

2. 0-47 0-80

These have little or no fertilising value.

Ash 'pit refuse. This material is naturally very variable
in composition. On the whole it is not particularly useful
as a fertiliser in spite of its smell: usually it contains
only about \ per cent, of nitrogen, 2 per cent, of potash
and about 1 per cent, of phosphate. On heavy land it
has advantages over and above its fertiliser content, as
it makes the soil lighter and more workable.

Sewage and seivage sludge.

It is estimated^ that the population of the United
Kingdom consumed before the war 1,438,000 metric
tons 2 per annum of protein containing 230,000 tons of
nitrogen. Most of this is excreted and a considerable
part appears in sewage. Assuming the population to
have been 45-2 millions, and disregarding the nitrogen
in the growth increase, this gives a yearly average of
11 lbs. nitrogen excreted per head of the population.
Of this 86 per cent, is in the urine and 14 per cent, in the
faeces. Data for potash and phosphates do not exist, but
assuming that these were about one quarter the value
of the nitrogen figures the fertiliser value per annum of

^ Food Supply of the United Kingdom: Roy. Soc. Repf., 1917, Cd. 8421.
^ A metric ton = 1000 kilos = 2205 lbs.

204

Fertilisers

[PT. Ill

the excrements of the population of the United Kingdom
would be:

Nitrogen

P.O5 K,0

Value per annum"^

Total, tons per

annum
Average, lbs. per

head per annum

230,000
11«

57,000

57,000
2|

£17,590,000
75. 9^.

This is approximately equal to the value of farmyard
manure and all the other fertilisers put together (p. 217).
Owing to various losses, however, only a small part of
this ever reaches the sewage works. An average
quantity of domestic sewage is 33 gallons per head per
day, containing 5 parts of nitrogen per 100,000; this
corresponds to 6 lbs. of nitrogen per head per annum.
Further, only a portion of the population is connected
with sewage systems. Unfortunately no practicable
means of realising the value of sewage has yet been
devised. Broad irrigation and sewage farming answer
under certain conditions, but not as general methods of
treatment. The only material generally available is the
sludge which is prepared by some precipitating or settling
process, and therefore contains only the insoluble com-
pounds and not the soluble and valuable nitrates,
ammonia, etc. This indeed is its weakness: it has been
so well washed during the process of formation that it
has lost much of its decomposable material.

Various experiments have frequently been made to
ascertain the manurial value of sludge, but the results

* When sulphate of ammonia =£14 per ton; 30% super =£3; and
sulphate of potash = £12.

" Tills being the average, the figure is naturally higher for adults. Thus
it is estimated that an adult excretes 50 ozs. of urine daily, containing
1 % of nitrogen: this alone amounts to 11 lbs. per annum.

CH. xi] Activated Sewage Sludge 205

have not been very satisfactory. The usual course of
events is that farmers are first induced to purchase it
but finally have to be paid to take it away. Methods
have therefore been devised for improving the sludge,
perhaps the commonest being to add a certain pro-
portion of lime and then to force the mass into presses
when it forms a cake containing roughly 50 per cent,
of water, 15 to 25 per cent, of organic matter and
25 to 35 per cent, of mineral matter much of which
is lime, and about 1 per cent, each of nitrogen and of
P2O5. Several of these pressed sludges were tested on
field crops during the years 1905-8, but the results were
not good: only in the wetter districts of the North of
England did they seem to have much value^. In some
places, e.g., Glasgow, Kingston, etc., other materials are
added to enrich the sludge. These and other sludges
are sent out in good mechanical condition ready for
distribution: but some of them suffer from the draw-
back that they are sold at prices considerably in excess
of their real value. At Bradford and Huddersfield a
process is at work to extract the fat, grease, etc., which
in modern times have become too precious to lose even
in sewage ; the resulting products contain respectively
2 and 3| per cent, of nitrogen and are of distinct
fertiliser value.

A recent process consists in blowing air through the
sewage; this gives a sludge very different in character
from the older types and containing as much as 6 per
cent, or more of nitrogen and over 4 per cent, of P2O5.
The material is called activated sludge and is said to be
of high manurial value 2.

^ 5th Report of the Sewage Commission, 8th Appendix, Cd. 4286, 1908.
A good summary is given in Journ. Board of Agric, 1908, xv. p. 690.
2 E. Ardern, Journ. Soc. Chem. Ind., Jan. 31, 1917 and July 31, 1917.

CETAPTER XII

THE PURCHASE AND USE OF ARTIFICIAL MANURES

The British farmer has a fairly wide range of fertihsers
to select from, and in addition he fertilises his land
through the feeding stuffs purchased for his cattle. The
supplies are regularised by the various syndicates, never-
theless there are market fluctuations of which farmers
and co-operative societies should take advantage. Fur-
ther, a large number of proprietary manures are on the
market, the percentage analysis of which has to be de-
clared^, and it is therefore convenient to have a method
by which one fertiliser can be compared with another
to ascertain which is the cheaper.

The basis of comparison is the unit value. A unit is
1 per cent, per ton ; the unit value is the cost of 1 per
cent, per ton, and it is obtained by dividing the cost of
the manure by the percentage of nitrogen, potash or
phosphate. Thus the unit value of nitrogen in nitrate
of soda is obtained as follows :

Nitrate of soda contains 15 per cent, of nitrogen and
cost before the war £11 f.o.r.

.*. 1 per cent, cost £\^ per ton = 145. 8r/.

and this was the unit price or unit value. So the unit
value of nitrogen in sulphate of ammonia was
price per ton £13

percentage of nitrogen 20

135.

1 Under the Fertilisers and Feeding Stuffs Act, 1906, full details of
which are given in the Journ. Board of Agric, 1906-7, x. 13; and of the.
Compound Fertiliser Orders of the Ministry of Munitions.

FT. Ill, CH. xii] Unit Prices 207

In this case the sulphate of ammonia was the cheaper
and would have been purchased unless there were any
special reason for choosing the nitrate of soda.

The unit value of phosphate in superphosphate or in
basic slag, and of potash in the various potash fertilisers,
is obtained in the same way.

When manures contain two or more fertilising con-
stituents it is obviously impossible to proceed entirely
in this wsij, and certain conventions have to be adopted.
It is assumed that the potash has the same value as in
the potash fertilisers but that insoluble phosphate has
less value than in superphosphate, an assumption that
is probably sound. The actual value assigned to the
phosphate before the war was usually about \s. 3d. to
Is. 9d. according to the grade of the manure; guanos,
fish and meat meal ranking higher than steamed bone
flour. After allowing for these two constituents one can
proceed to calculate the unit value of the nitrogen :

A Peruvian guano containing^ 7 per cent, of ammonia
{i.e., 5- 8 per cent, of nitrogen), 30 percent, of phosphates
and 2 of KoO, was offered at £9. 125. 6c?. per ton f.o.r.

1 unit of phosphate was worth Is. 9d. £ s. d.

.: 30 were worth 2 12 6
1 unit of KoO was worth 4*. 6d.

.". 2 were worth 9 0

The phosphate and KoO were worth ... 3 1 6

.•. For 5-8 per cent, of nitrogen the dealers
were asking £9. 125. 6d. less £3. Is. U. 6 11 0

i.e., unit price asked = 225. Id.
The advantage of the unit system is that it at once

^ The trade expression. See pp. 143 and 150.

208

Fertilisei's

[PT. in

enables a buyer to discriminate between a cheap and a
costly article. The following is an actual illustration:

A proprietary manure, containing 1-8 per cent, of
nitrogen, 22 per cent, of phosphate, and 2 of K2O, was
offered before the war at £5. 55. per ton.

£

s.

d.

1

11

0

9

0

22 units of phosphates were @ I*. 5d. worth
2 „ K2O „ 4:S.e,d. „

The phosphates and K2O were worth ... 2 0 0
.•. For 1-8 per cent, of N the dealers were

asking ... ... ... ... 3 5 0

■i.e., unit price asked = 365. Id.

which is clearly excessive. Further instances of excessive
price for low grade manures can be fomid in the agri-
cultural journals^.

Many dealers give the percentages of ammonia instead
of nitrogen. Table XVIII is useful for the purpose of con-
version :

Table XVIII. Conversion of percentages of nitrogen to
equivalent percentages of ammonia, and vice versa

Nitrogen to

ammonia

Ammonia to

nitrogen

er cent, of

Equivalent
per cent, of

Per cent, of

Equivalent
per cent, of

nitrogen

ammonia

ammonia

nitrogen

1

1-2

1

0-8

2

2-4

2

1-6

3

3-6

3

2-5

4

4-8

4

3-3

5

61

6

41

6

7-3

6

60

7

8-5

7

5-8

8

9-7

8

6-6

9

10-9

9

7-4

10

12-1

10

8-2

^ See Dr Voelcker's Reports in the Journal of the Royal Agricultural
Society, and Board of Agric. Leaflet, No. 270.

CH. xii] Mixed Manures 209

Mixed manures and pro'prietai'y articles. A farmer
who knows precisely what mixture of manures he wants
can get it made up without difficulty by the merchant,
but for those who are uncertain what to use, there
are advantages in purchasing mixed manures and a
number of good articles are on the market.

Since 1917 the Ministry of Munitions has controlled
the manufacture of Compound Fertilisers by Orders
issued under the Defence of the Realm Act, and manu-
facturers are compelled to declare not only the total
percentage of nitrogen, phosphates and potash, but also
the classes to which these constituents belong. The
Unit Rates fixed by the Order at present in force are :

Part I. Nitrogen

Class 1. Unit rate

Derived from sulphate of ammonia, salts of ammonia, nitrate of
soda, or other salts of nitric acid, cyanamide, meat, blood,
bone, slaughterhouse refuse, ground horn, ground hoof, guano,
fish offal, fish meal, fish guano, oil seeds, cakes or meals, or
dissolved shoddy, dissolved wool waste or dissolved silk waste
as below defined . . . . . . . . .18*. 6d.

Note. The expressions "dissolved shoddy," "dissolved wool
waste" and "dissolved silk waste" shall mean shoddy, wool
waste and silk waste treated with sulphuric acid or any similar
reagent in such a way that at least 80 per cent, of the fibre is
destroyed.

Class 2.
Derived from other sources Is. Qd

Part II. PJiosphates
Description.
"Water soluble," t.e. rendered soluble in water . . .4s. 3d.
"Citric soluble," i.e. insoluble in water, but soluble in a 2 per
cent, solution of citric acid in the manner prescribed by the
Fertihser and Feeding Stuffs (Method of Analysis) Regula-
tions, 1908 2s. 6d.

R. s. 14

210 Fertilisers [pt. in

Unit rate
"Insoluble," i.e. insoluble either in water or in a 2 per cent,
solution of citric acid in the manner prescribed by the said
Regulations \s. 6d.

Part III. Potash
Description.
"Soluble," i.e. soluble by the methods prescribed by the Regu-
lations 25s. Od.

In addition 255. per ton is allowed for mixing, bagging,
etc., and a further charge for credit.

Thus, the price per ton of a Compound Fertiliser of

the following composition :

Nitrogen 4 per cent, (of which 3 in Class 1).
Phosphates 20 per cent, (of which 15 soluble in water.

4 in citric acid, and 1 insoluble).
Potash 2 per cent.

would be:

5.

d.

£ s.

d.

•

Nitrogen

3 at 18

6

2 15

6

»j

1

7

6

7

6

Phosphates

15

4

3

3 3

9

99

4

2

6

10

0

99

1

1

6

1-

■ 6

Potash
Basis price

2

25

0

2 10

0

9 8

3

Mixing, bags

, ba:

gging

, etc.

1 5

0

10 13

3

This is the net cash price, and if any addition is made
for credit its amount must be distinctly stated.

The Order does not apply to mixtures made up to the
farmer's specification.

As a rule Compound Fertilisers in England contain
about 3 per cent, of nitrogen, and in Scotland a little
more. The best makers use only Class I nitrogenous
materials.

CH. XII J Manures for Crops 211

Manures for crops. No definite scheme for manuring
crops can be given for universal use because of the
varjdng factors of soil, climate, market prices, and
available capital, but certain guiding principles hold
fairly generally and can be adapted to each locaHty.

All of the fertilising constituents, nitrogen, potash,
phosphoric acid, lime and organic matter must be
applied to the land in the course of the rotation. The
nitrogen being liable to loss should be distributed, a
certain amount being added either each year or each
alternate year: the other four constituents are less liable
to loss and may be applied to any crop that is most
convenient. The Saxmundham experiments show that
equal financial returns are obtained wherever super-
phosphate is applied in the rotation, while nitrate of
soda could not be used in this indiscriminate manner
but gave better returns when applied to roots or wheat
than to barley. In practice it is usual to give a good
dressing to the root crop and lighter dressings to the
intervening cereal crops. Care has to be taken, also, to
avoid unequal intervals between dunging and folding
the land. The distribution of manure is often effected
somewhat as follows :

The root crop commonly receives a mixture of farm-
yard manure and a complete dressing of artificials, phos-
phates preponderating in the mixture for swedes, tur-
nips, rape, etc., while potash forms a larger proportion
of the dressing given to mangolds, sugar beet, and
potatoes. It should be stated, however, that direct
experiments have rarely justified the use of artificials in
addition to farmyard manure for swedes.

The succeeding cereal crop may be wheat or oats,
in which case it may need a little nitrogen in spring

14—2

212

Fertilisers

[PT. Ill

applied as nitrate of soda or of lime, sulphate of am-
monia, etc. ; in late districts or wet seasons super-
phosphate, etc., may be desirable to hasten ripening.
When the roots have been folded and barley is to be

without Nitrogen.
A.

With Nitrogen

Cwt. per Ace
50

Plots

Fig. 38. Effect of manures on the yield of hay. The Park,
Rothamsted. (Average 57 years, 1856-1912.)

Plots 3 and 12. Unmanured. Plot 4-1. Superphosphate only.

Plot 8. Superphosphate, sodium and magnesium salts.

,, 7. ,, ,, ,, + potassium salts.-

„ 4-2. Super and ammonium salts (86 lbs. N per acre).

,, iO Super and ammonium salts + sodium and magnesium salts.

,, 9. Super and ammonium salts + sodium and magnesium salts
+ potassium salts.

CH. xii] Manures for Grass Land 213

grown, no nitrogen is needed but superphosphate must
be appHed to prevent rankness (see p. 145).

The seeds may receive lime, basic slag or potash ; no
nitrogen is usually necessary where the aftermath is
folded off.

The grazing land should periodically receive basic
slag alone, or basic slag and kainit, while land laid in
for hay should in addition receive an annual dressing
of a nitrogenous manure such as sulphate of ammonia,
nitrate of soda, etc. : every four years or so, however,
dung should be applied instead. Fig. 38 shows the
results obtained at Rothamsted.

No general recipes can be given for the composition
of manures. At one time it was supposed that the ideal
mixture was that represented by the composition of the
ash as showing what the plant had actually taken from
the soil. This is now known to be incorrect: the need
for manures is determined not by the composition of the
plant but by its habit of growth and the conditions
under which it lives. On any particular farm the most
suitable mixtures can only be discovered by trial ; several
recipes can be drawn up on the basis of the information
already given, and the most suitable ones tested. The
problem is considerably simpHfied in counties where a
soil survey has been made or systematic field experi-
ments conducted.

Numerous field experiments have been made to dis-
cover the effects of the different fertilisers in various
districts: these have been summarised in the writer's
Manuring for Higher Crop Production. The following
increases have been obtained per cwt. of phosphate and
nitrogenous manures respectively:

214

Fertilisers

[PT. Ill

Wheat, grain
,, straw

Barley, grain
„ straw

Oats, grain
„ straw

Hay

Mangolds

Swedes

Potatoes

Per 1 cwt. super-
phosphate or high
grade basic slag

0-li bush.
^5 cwt.
2-3 bush.
0-2 cwt.
1-3^ bush.
0-2 cwt.

20 „

20-40 „

10 „

Per 1 cwt. sulphate

of ammonia or
nitrate of soda, or
1^ cwt. nitrohm
4J bush.
5 cwt.
6i bush.

7

6

8-10

32

20

20

6^ cwt.

bush,
cwt.

The actual amount of the mixtures that may be used
is regulated by the following general rule :

Additional manure usually gives extra crops (pro-
vided it is suitable) but beyond a certain point the yield
per cwt. of manure falls off, so that the extra crop is
obtained at higher cost per ton or per bushel than a
smaller crop would be. This is known as the Law of
Diminishing Returns, and it holds very generally; it is
just as true for the horse-power of a motor cycle as of
the yield of wheat. Table XIX gives an illustration
from the Broadbalk plots at Rothamsted:

Table XIX. hifluence of increasing dressings of nitro-
genous manures on yield of wheat; Broadbalk field.
Average 61 years, 1852-1912

-

Increase

Increase

Grain

per 200 lbs.

ammonium

salts

Straw

per 200 lbs.
ammonium

salts

bushels

bushels

cwts.

cwts.

Mineral manure alone

14-5

121

Mineral manure + 200

lbs. ammonium salts

23-2

8-7

21-4

9-3

Mineral manure +400

lbs. ammonium salts

321

8-9

32-9

II-5

Mineral manure + 600

lbs. ammonium salts

36-6

4-5

411

8-2

(See Figs. 2 and 39. )

Total Produce
per acre.

70001b.

6000

5000

4000

3000

2000

1000

Plots 3 4

Grain per Acre, lb. HHi Straw per Acre, lb.

Fig. 39. Diagram showing effect of increasing amounts of nitrogenous
manures on the yield of wheat. Broadbalk field, Rothamsted.
(Average 61 years, 1852-1912.)
Plots 3 and 4. Unmanured.

Plot 5. Potash and phosphates but no nitrogenous manure.
„ 6. Potash and phosphates and sulphate of ammonia containing

43 lbs. N per acre.
„ 7. Potash and phosphates and sulphate of ammonia containing

86 lbs. N per acre.
„ 8. Potash and phosphates and sulphate of ammonia containing

129 lbs. N per acre.
The columns represent total produce per acre, but the figures in the
dia-nond spaces give bushels of grain and cwts. of straw per acre

216

Fertilisers

[PT. Ill

Thus for the first 400 lbs. of ammonium salts each
100 lbs. gives an additional 4| bushels of wheat and
5 cwts. of straw, together worth about 405. : the dressing
has therefore been profitable : when more ammonium salts
are added the increase given by each lOOlbs. is worth only

11-

1912

1911

10-

1910

A

A

o

•c

§, 7-

A

•

a

B

'c '■

B

cS

n 5 •

B

OT

C

C

fi 41
o

C

D

a „

D

o 3-
3

D

S 2-

H-

E

-F

H-

E

^F

E

1 .

-F

G

G

H-

G

A = Superphosphate.

B = Mineral phosphate.

C = Potash salts.

D= Basic slag.

E= Nitrate of soda.

F = Sulphate of ammonia.

G=: Potash salts (as pure
potash).

H= Artificial nitrogenous
manures (nitrohm,
nitrate of lime),

I = Peruvian guano.

I I I

Fig. 40. The world's annual consumption of artificial fertilisers (from
Production et Consommation dcs Engrais CImniques, Institut Inter-
national d' Agriculture, Rome, 1914).

Each of the above columns is to be read from the base hne.

about 205, which is less profitable and in pre-war daj^s un-
profitable. On other soils the point of diminishing profit
may come somewhere else, but there always is such a
point, and the farmer must be careful not to pass it.

Application of artificial manures. The following points
are to be remembered :

CH. xii] Consumption of FertUisers 217

Nitrate of soda should go on as a top dressing after
the crop is up.

Sulphate of ammonia should go on just before the
crop is up except in the case of wheat and winter oats,
when it may be added as a top dressing in spring.

Superphosphate, potassic fertilisers and slag can go
on whenever convenient but should be applied not later
than early spring.

Labour may be saved by mixing the fertilisers when
two or more are to be drilled in or distributed, but the
following should not be mixed by the farmer:

Basic slag, lime or chalk with sulphate of ammonia.

Dissolved bones with nitrate of soda.

The following can be mixed if they are applied with-
out delay :

Superphosphate with nitrate of soda ; dissolved bones
with potash manures; basic slag with kainit.

All artificial manures have to be stored in a dry place
and mixed on a hard dry floor.

Fig. 40 shows the amounts of artificial manures pro-
duced annually before the Avar in all countries of the
world. The quantities used in the United Kingdom were
about one-tenth of these values : they were as follows :

Estimated pre-war Estimated

consumption in annual value

United Kingdom pre-war prices

tons per annum £
Farmyard manure

Nitrate of soda
Sulphate of ammonia . .
Cyanamide (nitrolim) and nitrate of lime
Superphosphate
Basic slag-
Guano ...
Bones . .
Others ...

Total

^ No good estimate can be made of the amount of guano, bones, and
other materials used as fertilisers.

... 37,000,000

11,000,000

80,000

920,000

60,000

750,000

lime 10,000

110,000

600,000

1,650,000

280,000

560,000

sayi 25,000

250,000

sayi 40,000

200,000

sayi 10,000

100,000

... 1,105,000

4,540,000

218 Fertilisers [pt. iii, ch. xii

Belgium, Luxemburg and Germany used more arti-
ficial manures than we did, their consumption being:

Amounts of fertiliser used in cwts. per acre

Great
Belgium Luxemburg Germany Britain

Phosphatio MO 1-36 0-66 0-6

Potassic 0-16 0-21 0-50 007

Nitrogen 0-55 0-07 0-18 0-10

Total artificial fertiliser 2-18* 1-64 1-34 0-771

' 0-9 according to other estimates.
* Including compound manures 0-37.

The potassic fertiUser is reckoned as containing 25 per cent. KjO.

Another estimate for British and German consumption closely agreeing
with the above is given in T. H. Middleton's German Agriculture (Cd.
8305), p. 36, where the phosphatic and nitrogen fertiUsers are calculated
as 30 per cent, superphosphate and sulphate of ammonia respectively.

This table, however, takes no account of the large
quantities of farmyard manure produced by the use of
feeding cakes imported from other countries, which in
our case are very large.

CHAPTER XIII

CHALK, LIMESTONE AND LIME

Chalk is one of the oldest fertilisers in this country
and was used by the ancient Britons in much the same
way as is still done in parts of Hertfordshire to-day^.

It has two main types of action: it supplies basic
material which is very necessary for the soil, and it
improves the physical condition. The necessity for a
base is very definitely marked: in its absence the soil
becomes "sour." Such soil is not well suited to plant
growth and will not carry luxuriant crops: certain
weeds, however, grow well, notably sorrel on heavy
land and spurry on light land. "Sourness" often arises
through neglect, though it also comes when land lies
waterlogged for a long time. The distinction between
"sour" soil and sweet soil is very great, for "sourness"
is not only inimical to plants but also to micro-organ-
isms, and the differences seen in vegetation are probably
no greater than those existing in the microscopic popu-
lation of the two soils. Just as certain weeds turn up
most commonly on "sour" soils so also do certain micro-
organisms, such as Plasmodiophora which causes finger
and toe in turnips and other plants of the Brassica tribe.
Wliatever the cause, the trouble can be put right by
suitable dressings of chalk or lime.

The alteration in physical condition has been more
fully studied, but is still somewhat obscure. It is mainly

1 See the author's Fertility of the Soil, Cambridge Manuals, and Journ.
Board of Agriculture, 1916, xxni. 625, for fuller details.

220 Fertilisers [pt. hi

attributed to the conversion of the deflocoulated or
sticky clay into the flocculated form. While in practice
chalk brings about this change it is not the actual agent
concerned in the deflocculation, indeed in the presence
of clay alone it is inert. It is effective only in presence
of a little carbonic acid which always occurs in the soil
and which causes it to go into solution as calcium bicar-
bonate (p. 25); this appears to be the effective agent.

Of course where the bad physical condition is due to
other causes chalk may be unable to put it right. The
silty clays form a case in point (p. 23).

In common with many other substances calcium bi-
carbonate is absorbed from its solution by certain con-
stituents of the soil, and displaces some of the substances
previously absorbed. Thus chalk causes the liberation
of a certain amount of potash from the soil so that a
dressing of chalk is often equivalent to a dressing of
potassic fertiUser.

Chalk increases the amount of bacterial action and
therefore the rate of nitrate production in the soil. If
much organic matter is present, it increases also the
amount of phosphate available for the plant^.

Limestone has the same chemical composition as
chalk, but it is much harder and does not readily dis-
solve in the soil water so that it cannot be used direct
in agriculture until it is ground. Mills were set up for
this purpose' as long ago as the eighteenth century, but
only recently have the mechanical difficulties been com-
pletely overcome and ground limestone put on the
market as a regular article of commerce.

It acts in precisely the same manner as chalk, and

^ British examples are common. An instance from Brittany is given
in Compt. Bend., 1917, clxiv. 409.

CH. xiii] Lime and O^'ganic Matter 221

when sufficiently finely divided goes further than chalk,
which is not usually ground.

Lime is chemically distinct from limestone or chalk,
being the oxide of calcium (CaO). It has certain charac-
teristic effects in the soil which neither of the other
substances produces. These effects, however, are only
transient since the lime is soon converted into carbonate,
and ultimately into bicarbonate, through the action of
the carbon dioxide always present.

It dissolves some of the organic compounds in the
soil and apparently effects a certain amount of decom-
position. This can be demonstrated by mixing 50 grams
soil with I to 1 gram of quick lime, adding 200 c.c. of
water and shaking weU. An extract tinged with yellow
or brown is obtained, which on analysis is found to
contain organic matter, potassium, and other substances.
Thus addition of excess of lime to the soil may result in
excessive decomposition and the loss of valuable plant
nutrients.

"Lime and lime without manure
Will make both farm and farmer poor,"

as the old saying goes^. One result of this decomposition
apparently is to aid the work of the soil bacteria and to
increase the production of plant food.

^ This was well known on the continent. Heresbach (Rei Rusticae libri
quatuor 1594) wrote "Vulgo dici solet, earn rationem stercorandi calce,
opulentos parentes, et hberos reddere inopes" which Googe translated
"The common people have a speach, that ground enriched with Chalke,
makes a rich father, and a beggerly sonne."

In the Pennsylvania State College experiments, plots annually re-
ceiving hme for 25 years contained less nitrogen by 375 lbs. per acre than
the plot receiving limestone. In the Virginia experiments the limed plot
was found to contain less nitrogen and less organic matter than the un-
limed plots.

222 Fertilisers [pt, hi

The second difference between lime and chalk is that
when added in sufficient quantity quicklime partially
sterilises the soil, killing many of the bacteria, protozoa
and other organisms^; later on the bacterial numbers
rise very considerably^ and produce increased quantities
of ammonia and nitrates; this stage coincides with the
time at which the lime is converted into calcium car-
bonate.

A third characteristic of lime is that, being an alkali,
it deflocculates the clay in heavy soils. This action,
however, is speedily reversed: as soon as conversion
into bicarbonate is complete the clay is flocculated and
the soil changed into the desirable crumbly state.

Effect on crop prochiction . The various improvements
set out above fall into two groups : semi-permanent and
transitory. When chalk or lime neutrahses sourness or
acidity, kills disease organisms or flocculates clay, it
produces an improvement which lasts for a long time,
at any rate until the undesirable condition is set up
again. In these cases the lime throws out of action a
harmful factor and raises fertility accordingly.

The value of lime in neutralising a harmful factor is
well shown at Rothamsted, at Woburn and at Cockle
Park. At Rothamsted sulphate of ammonia is applied
to some of the grass every year in such quantities that
the soil has become acid, and consequently unsuited to
the growth of some of the better grasses and clovers.
Lime neutralises this acidity and therefore restores the
soil to its normal neutral condition; the effect lasts so
long as the soil does not again become acid. Similarly
at Woburn a dressing of lime counteracts the acidity,
and therefore the sterility, produced by excessive use of

^ Hutchinson and MacLennan, Journ. Agric. Sci., 1914, vi. 302.

CH. xiii] Effects of Lime 223

sulphate of ammonia, and the effect persists. At Cockle
Park the lime was used to counteract finger and toe,
and here again it brought about an improvement in
crop which lasted for a considerable time.

Lime also effects a semi-permanent improvement on
wet, heavy soil as soon as adequate provision is made
for drainage, e.g., on the yellowish, greyish or blue clays
of the Lias and other formations of the Midlands, and
the heavy soils on the Mountain Limestone of the West ;
wherever, in short, owing to neglect in the past, the
drains and ditches have been stopped and the land has
consequently become thoroughly sour, as shown by the
predominance of bent, sheep's fescue and sweet vernal
grass (the two latter marked with very dark green
patches), sorrel, buttercups, hassocks, etc. The effect
of lime is to bring about a marked improvement in the
herbage which lasts until through neglect or bad
management the harmful conditions are allowed to set
up again.

Where there is no particularly harmful factor to be
thrown out of action, the effect of lime is by no means
so persistent. Thus lime only produced an effect in the
first year on the Rothamsted grass plot manured in the
sort of way a good farmer might adopt, i.e., dressed
with farmyard manure every fourth year and with
something else (fish guano in this case) two years after-
wards. It was quite a good effect, increasing the yield
of hay from 41 to 63 cwts. per acre, but it only lasted
one season. Here the herbage had been quite satis-
factory and there was no specially harmful condition in
the soil. On the other hand, a plot on the same field
that had been rendered acid by excessive use of sulphate
of ammonia showed increases for at least four years

224 Fertilisers [pt. hi

because the special harmful factor — the acidity — was
overcome.

Qiiantity required. Where a harmful factor has to be
thrown out of action the dressing of lime or chalk must
be sufficient for this purpose. Where no special function
is to be served much less is needed. Certain analytical
methods have proved helpful in indicating the quantity
needed to counteract acidity^ and there are data for
showing how much is needed for maintaining fertility
generally. Since lime and chalk are both converted into
soluble calcium bicarbonate in the soil they are liable
to be washed out. There are sources of production in
the soil, but the general tendency is for losses to pre-
ponderate, and at Rothamsted they amount to some
800 lbs. of lime (CaO) per acre per annum on arable
land but less on grass land; very similar results were
obtained by Hopkins in Illinois. This amount would be
returned to the soil in 8 cwts. of good burnt lime (85
per cent. CaO) or 15 cwts. of limestone or chalk and if
this dressing were annually given per acre there would
be no diminution in the stock. Lime and limestone can
readily be had in a finely divided state, and can be put
on with a distributor as a regular proceeding: 1 ton of
lime or 2 tons of limestone are suitable quantities. Cob
lime may be used instead of ground lime and is cheaper,
but on the other hand it is more costly to spread. Chalk
is not easy to grind and is usually applied in lumps, less
than 20 or 30 tons per acre cannot conveniently be
added so that regular dressings are not common, and it
is only put on at long intervals when other work allows,
which means in practice that chalking is commonly

^ E.g. those of Veitch {Journ. Amer. Chem. Soc, 1902, xxiv. 1120), and
of Hutchinson and MacLennan {Journ. Agric. Science, 1915, vu. 75-105).

CH. xiii] Lime and Limestone 225

neglected. There is no doubt that neither liming nor
chalking is done as regularly as it should be, and that
fertility is suffering in consequence.

One of the first steps to be taken in improving run
out land is to apply lime or chalk and in some countries
facilities for doing this are afforded by the State: e.g., in
Illinois limestone is ground at the State Penitentiaries
and sold at a very cheap rate to farmers, Clay soils in
particular stand in need of lime, because of their ten-
dency to become deflocculated, but sandy soils also re-
quire dressings because they readily become sour.

Lime has usually proved inferior to ground lime-
stone in the long series of experiments at the Maryland
Experiment Station^ and in the still longer series at
the Pennsylvania Experiment Station^. Milburn and
Gaut obtained similar results in the Lancashire trials^.
This inferiority, however, is sometimes outweighed by
another consideration: 1 cwt. of lime is equivalent to
If cwts. of ground limestone and this difference becomes
important where freight is high. Limestone can be kept
in bags but lime must be used as soon as possible.
Instead of lime the farmer may sometimes be able to
buy lime ashes or trade wastes cheaply, but he should
only do this after an analysis has been made.

Ground limestone or lime should be applied in
autumn or early spring and may with advantage be
put on to the clover crop or to turnips : both crops re-
spond well, indeed clover (and other leguminosse) will
often fail when lime is deficient in the soil while turnips
or swedes become liable to finger and toe. The potato
crop, however, does not usually benefit except on very

1 Bull. No. 110, 1906. 2 Annual Report, 1907-8, p. 93.

» Lancashire C. C, Bull. No. 2-t, 1914.

E. s. 15

226 ^ Fertilisers [pt. hi, ch. xiii

sour land, and the liability to scab is considered by some
practical men to increase after lime is applied, but more
definite experiments are needed on the subject. Rhubarb
does not usually benefit.

Chalk should be applied as early as possible in autumn
so that winter frosts can disintegrate it and allow of a
better distribution later on by means of the harrow : it
is most conveniently applied to the leys.

Even where limestone does not increase the jdeld of hay
or grass land it may improve the herbage : this happened
at Garforth, where sorrel was crowded out, and also in the
Lancashire trials, where the bent grass was practically
exterminated while the rye grass practically doubled.

Many limestones contain magnesia and are therefore
considered to be risky in use ; the Newcastle Farmers Club
allows compensation for eight years for ordinary lime^
but nothing for lime derived from magnesian limestone.
The experiments hitherto made in this country have
not justified this view nor have those at New Jersey^.

Mortar rubbish contains considerable quantities of
calcium carbonate and should always be applied to gar-
dens whenever it can be obtained: it not only benefits
the soil but in virtue of its sand it helps the development
of fibrous root.

Magnesian hme has proved useful on heavy soils
though it has sometimes given trouble on light land^.

Gas lime may be used with advantage when it can be
obtained cheaply, but it should only be applied in
winter. The modern variety is less offensive than the
old fashioned "Blue Billy" but it is less useful as an
insecticide in horticultural work.

* Durham Coll. Bull. No. 12, 1915.

New Jersey Bulletin, No. 267, 1914.
» See J. A. Hanley, Jo'irn. Soc. Chem. Ind. 191S, 18.5 T.

APPENDIX

THE METHODS OF SOIL ANALYSIS

(L

1

^

How to take a sample of soil. Owing to the variation in com-
position of the soil at different depths it is particularly necessary
that the sample should always be taken to the same depth and with
a tool making a clean vertical cut. Samples taken with a spade are
of very doubtful value and do not justify any lengthy examination.
The simplest tool is shown in Fig. 41 and consists of a steel tube
2 in. in diameter and 12 in. long, with a f in. slit cut along its length
and all its edges sharpened. The tube is fixed on to a vertical steel
rod bent at the end to a ring 2 in. in
diameter, through which a stout wooden
handle passes. A mark is made 9 in. from
the bottom so that the boring process
can be stopped as soon as this depth is
reached. On withdrawing the tool the
core of soil is removed by a pointed iron
rod. Five or six samples should be taken
along lines crossing the field so as to get
as representative a sample as possible;
the whole bulk must then be sent to the
laboratory. The student should carefully
learn how to do this so that he can take
samples for himself. Samples should not
be taken from freshly ploughed or recently manured land.

The analysis. On arrival at the laboratory the soil is spread out
to dry, and is then pounded up with a wooden pestle and passed
through a 3 mm. sieve. The stones that do not pass through, and
the fine earth that does, are separately weighed, and the proportion
of stones to 100 of fine earth is calculated. Subsequent analytical
operations are made on the fine earth.

Moisture. Four or five grams of the soil are dried at 100° C. till
there is no further change in weight.

Organic matter. No accurate method of estimation has yet been
devised. It is usual to ignite at low redness the sample dried as

15—2

Fig. 41. Soil borer.

228 Apx)endix

above. The loss includes organic matter, water not given off at
100° C, and carbon dioxide from the carbonates; allowance maj' be
made for the latter, but not for the combined water.

Total nitrogen. Kjeldahl's method is almost invariably adopted.
About 25-30 grams of soil are ground up finely in an iron mortar;
10-15 grams are then heated in a Kjeldahl flask with 20-25 c.c.
of strong sulphuric acid for f hour; then 5 grams of potassium
sulphate are added, and shortly after a crystal of copper sulphate.
The heating is continued till all the black colour has gone. Then
cool and dilute the mixture, transfer the fluid part to a distillation
flask, but leave as much as possible of the sand behind, and wash
well to remove all the adhering liquid. Add saturated soda solution
till the liquid is strongly alkaline, distil and collect the ammonia in
standard acid.

Nitrate. Place 100 grams of soil in a stoppered bottle and shake
well with 100 c.c. of water. After waiting for the heavier particles
to settle, decant some of the extract through a filter. Evaporate
10 c.c. of the filtrate to dryness on a water-bath and add 1 c.c. of
phenol sulphonic acid (made by adding 55-5 c.c. of strong pure
H2SO4 to 4-5 c.c. of water containing 9 grams of phenol) to the
residue, stirring well with a small glass rod. After 10 minutes dilute
with 25 c.c. of water and add ammonia or caustic potash till alkaline
to litmus paper. If nitrate is present the solution becomes bright
yellow, the depth of the colour being proportional to the amount of
nitrate. The colour should be compared with that produced by 10 c.c.
of a solution of nitrate of soda containing 10 parts of nitrogen per
million, i.e., 0-06 gram of the salt per litre. A safety pipette should
be used for the phenol sulphonic acid.

For more accurate work reduce the extract with a zinc-copper
couple, distil off the ammonia with standard acid and titrate.

Carbonates are determined by treating a weighed quantity of the
soil with dilute sulphuric acid and estimating the carbon dioxide
evolved. Large quantities can be determined rapidly and accurately
by Collin's calcimeter (p. 27). Small quantities can be estimated by
absorbing the CO2 in potash and determining the amount by titration.
Forms of apparatus are described by Amos, Journ. Agric. Science,
1905, I. 322-326, Hutchinson and MacLennan, Journ. Agric. Science,
1914, VI. 323, and others.

Mineral substances. Complete analysis of a soil after the" silicates

Appendix 229

have been decomposed and the silica volatilised by treatment with
hydrofluoric acid is only rarely attempted. The British method,
adopted by the Agricultural Education Association, is thus described
by Hall: "20 grams of the powdered soil are placed in a flask of Jena
glass, covered with about 70 c.c. of strong hydrochloric acid, and
boiled for a short time over a naked flame to bring it to constant
strength. The acid will now contain about 20-2 per cent, of pure
hydrogen chloride. The flask is loosely stoppered, placed on the
water-bath, and the contents allowed to digest for about forty-eight
hours. The solution is then cooled, diluted and filtered. The washed
residue is dried and weighed as the material insoluble in acids. The
solution is made up to 250 c.c. and ahquot portions are taken for the
various determinations. The analytical operations are carried out in
the usual manner, but special care must be taken to free the solution
from siUca or organic matter." {The Soil.) As a rule only potash and
phosphoric acid are determined, but where other bases are wanted
they are estimated in the usual way.

Potash. 50-100 c.c. of the solution are evaporated to dryness after
addition of 0-5 gram of pure CaCOg if the original soil did not effervesce
when HCl was added.

Add 10 c.c. of 5 per cent, baryta solution, evaporate to dryness,
ignite and take up with water, add 2-5 c.c. perchloric acid (sp. gr.
1-12), concentrate till dense fumes are given off, allow to cool, add
20 c.c. of 95 per cent, alcohol and stir. Decant off the clear alcohol, add
40 c.c. alcohol containing 0-2 per cent, perchloric acid, transfer to a
tared filter paper, wash with 50-100 c.c. of 95 per cent, alcohol till
the runnings are no longer acid, dry at 100° C, and weigh as KCIO4 .

Phosphoric acid. The charred residue from which the potassium
chloride has been removed is now extracted with hot dilute H2SO4,
the filtrate and washings amounting to about 110 c.c. Add 25 c.c. of
ammonium nitrate solution. Warm to 55° C, add 25 c.c. ammonium
molybdate solution also at 55°, stir, aUow to cool and filter after
standing two hours. Decant through a filter: wash by decantation
with 2 per cent. XaXOg till the washings are neutral, transfer the
precipitate to the beaker used for the precipitation, and add a known
volume of standard alkah so that the precipitate completely dissolves.
Measure the excess by titration using phenolphthalein as indicator.
1 C.C. of X/10 alkali = 00003004 gm. PjOj.

Ainilable potash avd phosphoric acid. Dyer's directions are as

230 Appendix

follows: 200 grams dry soil are placed in a Winchester quart bottle
with 2 litres of distilled water in which are dissolved 20 grams of
pure citric acid. The soil is allowed to remain in contact with the
solution at ordinary temperatures for seven days, and is shaken a
number of times each day. The solution is then filtered, and 500 c.c.
taken for each determination; this is evaporated to dryness, and
gently incinerated at a low temperature. The residue is dissolved
in hydrochloric acid, evaporated to dryness, redissolved, and filtered ;
in the filtrate the potash is determined as above. For the phosphoric
acid determination the last solution is made as before, with the nitric
acid; then proceed as above.

Mechanical analysis. 1. Ten grams of the air-dry earth, which
has passed a 3 mm. sieve, are weighed out into a porcelain basin
and worked up with 100 c.c. of is/5 hydrochloric acid, the acid being
renewed if much calcium carbonate is present. After standing in
contact with the acid for one hour, the whole is thrown upon a dried,
tared filter and washed until free of acid. The filter and its contents
are dried and weighed. The loss represents hygroscopic moisture and
material dissolved by the acid.

2. The soil is now washed off the filter with dilute ammoniacal
water on to a small sieve of 100 meshes to the linear inch, the portion
passing through being collected in a beaker marked at 10, 8-5 and
7-5 cm. respectively from the bottom. The portion which remains
upon the sieve is dried and weighed. It is then divided into "fine
gravel" and "coarse sand" by means of a sieve with round holes of
1 mm. diameter. The portion which does not pass this sieve is the
"fine gravel." This should be dried and weighed. The difference
gives the "coarse sand." If required, both these fractions can also
be weighed after ignition.

3. The portion which passed the sieve of 100 meshes per hnear
inch is well worked up with a rubber pestle (made by inserting a glass
rod as handle into an inverted rubber stopper), and the beaker filled
up to the 8-5 cm. mark and allowed to stand twenty-four hours. The
ammoniacal liquid which contains the "clay" is then decanted oft'
into a Winchester quart. This operation is repeated as long as any
matter remains in suspension for twenty-four hours. The liquid
containing the "clay " is flocculated with hydrochloric acid. The dried
residue consists of "clay" and "soluble humus." After ignition the
residue gives the "clay" and the loss on ignition the "soluble humus."

Appendix 231

4. The sediment from which the "clay" has been removed is
worked up as before in the beaker, which is filled to the 10 cm.
mark and allowed to stand for 100 seconds. The operation is re-
peated till the "fine sand" settled in 100 seconds is clean, when it
is collected, dried and weighed.

5. The turbid Uquid poured off from the "fine sand" is collected
in a Winchester quart, or other suitable vessel, allowed to settle,
and the clear hquid syphoned or decanted off. The sediment is then
washed into the marked beaker and made up to the 7'5 cm. mark.
After stirring, it is allowed to settle for twelve and a half minutes;
and the liquid decanted off. The operation is then repeated as before
till all the sediment sinks in twelve and a half minutes leaving the
liquid quite clear. The sediment obtained is the "silt" which is dried
and weighed as usual. The hquid contains the "fine silt," which,
when it has settled down, can be separated by decanting off the!"
clear liquid and dried and weighed.

6. Determinations are made of the "moisture" and "loss on
ignition" of another 10 grams of the air-dry earth. The sum of the
weights of the fractions after ignition + loss on ignition + moisture
-I- material dissolved in weak acid should approximate to 10 grams.
The sizes of the particles thus sorted out are as follows:

Fine gravel ... ... Above 1 mm.

Coarse sand

Find sand

Silt

Fine silt . .

Clay

1 to 0-2 mm.
0-2 to 0-04 mm.
0-04 to 0-01 mm.
0-01 to 0-002 mm.
Below 0-002 mm.

Analysis of manures

The following are the official methods commonly adopted in this
country :

Thoroughly mix the sample, and if possible, pass it through a
1 mm. sieve. The percentage of moisture is determined by drying
a weighed sample at 100° C.

Nitrogen, {a) In the absence of nitrates and ammonium salts.
A weighed quantity of the sample is put into a Kjeldahl flask with
10 grm. of potassium sulphate and 25 c.c. of concentrated sulphvuric
acid; the flask is heated till the contents become colourless or of a
light straw colour. The operation may be accelerated by adding a

232 Appendix

small crystal of copper sulphate or a globule of mercury to the liquid
in the digestion flask. During the process the nitrogen compounds
are converted into ammonia, the amount of which is determined by
distillation into standard acid after liberation with alkaU, and, where
mercury has been used, with the addition also of sodium or potassium
sulphide solution. A blank experiment, using 1 gram of pure sugar
in place of the sample, is made in order to give the amount of nitrogen
present as impurity in the reagents used, which amount must be
deducted from the quantity found in the first experiment.

(6) In presence of nitrates. A weighed sample is put into the
K jeldahl flask with 30 c.c. of concentrated sulphuric acid, 1 gram of
salicyUc acid is added, and the flask shaken at intervals, but kept
cool; then 5 grm. of sodium thiosulphate and 10 grm. of potassium
sulphate are put in, and the flask heated till the contents are colour-
less or nearly so. The rest of the procedure is as before.

(c) Nitrogen as ammonia. Alkali is added, and the ammonia is
distilled into standard acid as above.

[d) Nitrogen as nitrates, ammonia and organic nitrogen heinq absent.
1 grm. of the sample is placed in a 500 c.c. Erlenmeyer flask with
50 c.c. of water. 10 grm. of reduced iron and 20 c.c. of sulphuric acid
of 1-35 sp. gr. are added. The flask is closed with a rubber stopper
pierced with a thistle tube the head of which is half-filled with glass
beads. The hquid is boiled for five minutes and the flask is then
removed from the flame, any liquid that may have accumulated
among the beads being rinsed back into the flask with water. The
solution is boiled for three minutes more, and the beads again
washed with a little water. The ammonia is then distiUed off and
estimated as before.

Phosphates, (a) Soluble in water. 20 grm. of the sample are
continuously shaken for thirty minutes in a htre flask with 800 c.c.
of water. The flask is then filled to the mark, again shaken, and the
contents filtered. 50 c.c. of the filtrate are boiled with 20 c.c. of
concentrated nitric acid, and the phosphoric acid determined by the
molybdate method below.

(b) Soluble in 2 per cent, citric acid solution. 5 grm. of the sample
are put into a stoppered bottle of about 1 litre capacity, and 500 c.c.
of a solution of citric acid, containing 10 grm. of the crystallised acid,
added. The bottle is shaken in a mechanical shaker for thirty
minutes. The solution is then poured all at once on to a large folded

Appendix ■ 233

filter, and the filtrate if not clear passed through the same paper
again. 50 c.c. of the filtrate are then taken and treated as directed
below.

(c) Total phosphoric acid. The nitric acid solution of a weighed
quantity of the sample, after destruction of the organic matter if
necessary, and removal of the silica by suitable means, is treated as
below.

(d) The molybdate method. To the solution obtained in (a), (6) or
(c), which should contain 0-1 to 0-2 grm. of P2O5, 100 to 150 c.c. of
molybdic acid solution are added, the whole warmed to 70° C. in a
water-bath for 15 minutes, allowed to cool, and filtered. The pre-
cipitate is washed first by decantation and afterwards on the filter
paper with 1 per cent, nitric acid; the filtrate and washings are set
aside and tested with more molybdic acid. The precipitate is dis-
solved in cold 2 per cent, ammonia solution, about 100 c.c. being
used for the purpose. 15 to 20 c.c. of magnesia mixture are then
added, drop by drop with constant stirring. After standing two
hours, with occasional stirring, the precipitate is filtered oi3, washed
with 2 per cent, ammonia, dried, ignited, and weighed as magnesium
pyrophosphate.

The molybdic acid solution. 125 grm. of molybdic acid and 100 c.c.
of water are placed in a litre flask, and the acid dissolved by the
addition, while shaking, of 300 c.c. of 8 per cent, ammonia. 400 grm.
of ammonium nitrate are added, the solution is made up to the mark
with water, and the whole added to 1 litre of nitric acid (sp. gr. 1-19).
It is maintained at about 35° C. for twenty-four hours and then
filtered.

Magnesia mixture. 110 grm. of crystallised magnesium chloride
and 140 grm. of ammonium chloride are dissolved in 1300 c.c. of
water. 700 c.c. of 8 per cent, ammonia are added, and the whole
allowed to stand for several days and filtered.

Ammonia solutions. (1) 8 per cent. 1 volume of ammonia solution
of sp. gr. 0-880 is mixed with 3 volumes of water and the solution
adjusted by addition of more water or ammonia till the sp. gr. is
0-967.

(2) 2 per cent. 1 volume of 8 per cent, ammonia is mixed with
3 volumes of water.

(This is the official method: the titration method given on p. 229
is simpler and equally accurate.)

234 AjJj^endix

Potash, (a) Muriate, free from, sulphate. A weighed quantity of
the sample — 5 grm. of a high-grade, 10 grm. of a low-grade muriate
is dissolved in water, and the solution, filtered if necessary, made up
to 500 c.c. To 50 c.c. of this a few drops of hydrochloric acid and
10 to 20 c.c. of a solution of platirric chloride containing 10 grm.
platinum in 100 c.c. water are added. Evaporate over the water-
bath to a syrup, cool, treat with alcohol of sp. gr. 0-864. Collect the
precipitate on a weighed filter paper, wash with alcohol as above,
dry at 100° C, and weigh.

Or, as a simpler and equally accurate process:

To 50 c.c. of the solution filtered from the 500 c.c. above add 7 to
12 c.c. of a 20 per cent, solution of perchloric acid (sp. gr. 1-125):
concentrate till white fumes are copiously evolved: redissolve the
precipitate in hot water: add 'a few drops of the perchloric acid
solution and again concentrate to the fuming stage. Cool. Stir the
residue with 20 c.c. alcohol of sp. gr. 0-816 to 0-812. Allow the pre-
cipitate to settle, filter by decantation through a weighed filter paper
or a Gooch crucible: wash with alcohol saturated with potassium
perchlorate; dry at 100° C. and weigh.

(6) 8alts containing sulphate. Boil a weighed quantity of the
sample (5 to 10 grm.) with about 300 c.c. water and 20 c.c. hydro-
chloric acid in a 500 c.c. flask. Barium chloride is added drop by
drop till precipitation of the sulphuric acid is complete. Any excess
of barium chloride is then removed by careful addition of sulphuric
acid. Cool, and make up to 500 c.c A portion of the solution is
filtered, the precipitate washed, and the potassium in 50 c.c. of the
filtrate determined as above either by the platinum chloride or the
perchlorate method: as in (a).

(c) Guxtnos, mixed fertilisers, etc. 10 grm. of the sample are gently
ignited to destroy organic matter, heated for 10 minutes with 10 c.c.
of concentrated hydrochloric acid, and finally boiled with 300 c.c.
water. Filter into a 500 c.c. flask, raise to the boiling point, and add
a slight excess of powdered barium hydrate. Cool, make up to
500 c.c, and filter. To 250 c.c. of the filtrate add ammonium hydrate
and ammonium carbonate, and then, while boiling, a little powdered
ammonium oxalate. Cool, make up to 500 c.c, and filter. Evaporate
100 c.c of the filtrate in a porcelain dish, heat the residue first in an
air-bath and then very gently over a low flame till all volatile matter
is driven off, but keep the temperature below dull redness. Moisten

Appendix 235

the residue with conceDtrated hydrochloric acid, evaporate to dry-
ness, treat with dilute hydrochloric acid, filter and wash, determine
the potash in the filtrate as in (a).

{d) Flue dusts. 10 grams are ignited gently to char organic
matter, then boiled with 300 c.c. water. Add 10 c.c. concentrated
hydrochloric acid slowly so as not to check the boihng ; then boil for
a further 10 minutes. Filter into a 500 c.c. flask and raise to boihng
point: add powdered barium hydroxide to slight excess, cool, make
up to 500 c.c, filter. To 250 c.c. of the filtrate add ammonia and
excess of ammonium carbonate, and, while boihng, a little powdered
ammonium oxalate. Cool, make up to 500 c.c. and filter. Evaporate
50 or 100 c.c. of the filtrate to dryness: heat the residue gently over
a low flame to expel ammonium salts, keeping the temperature care-
fully below redness. Moisten with concentrated hydrochloric acid,
evaporate to dryness, treat with dilute hydrochloric acid, filter,
determine the potash as in (a).

BIBLIOGRAPHY

The following books may be suggested to the student for further
reading: —

Hall, A. D. The Soil. (Murray.;!

,, Fertilisers and Manures. (Murray.)

Russell, E. J. Soil Conditions and Plant Growth. (Longmans.)
„ The Fertihty of the Soil. (Cambridge Press.)

„ Manuring for Higher Crop Production. (Cambridge

Press. )

Wood, T. B. Practical Exercises in Agricultural Chemistry.
(Cambridge Press.)

INDEX

Acidity in soils, 96

Air in soil, 30

Alkali soils, 54

American soils, some main groups,

54
Ammonia production in soils, 42 ;

nitrate of, use as fertiliser, 136 ;

sulphate of, use as fertiliser, 133
Ashpit refuse as manure, 203
Azotobacter, 45

Barber, Samalkota experiments,

167
Basic slag, 147; comparison with

superphosphate, 152
Berry, K. A. , on proper time to apply

farmyard manure, 185
Black soils, 40, 55
Blood, dried for manure, 195
Bones as fertilisers, 140
Bracken as litter, 169
Bracken ash as source of potash,

156

Cake feeding improves dung, 168,
ISO

Calcium carbonate, effect on soil,
219; in soil, estimation of, 228;
in soil, loss of, 50, 224. See also
Chalk

Calcium cyanamide asfertiliser, 137

Carr, 40

Catch crops, 63

Cattle and soil fertility, 117

Cellulose, decomposition in soil, 37

Chalk, as manure, 219; composition
and properties, 24 ; origin of, in
soil, 27; soils, 122. See also Cal-
cium carbonate

Clay, properties of, 21 ; soils, two
kinds, 108

Climate, effect in determining the

general character of the soil, 48;

effect in determining what crops

can he grown, 63
Climatic zones and soil belts,

52
Clover, effect on soil fertility, 45,

121
Clover sickness, 121
Cockle Park experiments with phos-

phatic fertilisers, 151, 153; with

potassic fertilisers, 163
Colloids, 21
Composts, 187
Compound fertilisers, 187
"Condition" of soil, 76
Conditions necessary for plant

growth, 2
Crop maps, 67, 68, 73
Crops, manures for different, 211
Crops suitable for different climatic

conditions, 64
Crops suitable for different soil,

48, 125
Cultivations, 63, 76
Cyanides, toxic effect of, 155

Darwin on earthworms, 85
Defiocculation of clay, 109
Denitrification, 44
Depth of soil, 97
Destructor dust as manure, 203
Diameters of soil particles, 16
Digger ploughs, 79
Diminishing returns, law of, 214
Disk cultivators, 85, 87, 111
Dissolved bones, 141
Dongas in S. Africa, 51
Drainage, 98; water, 50, 61
Drain gauges, 62
Dry farming, 74

23C

Index

Early crops, value of, 65
Earthing up, 88
Earthworms, effect on soil, 85
Economic factors in crop produc-
tion, 69
England, distribution of crops in, 72
English soils: some main groups,

56
Eroded lands of Australia, 51
Explosives, use for cultivation, 91

Fallowing, 89, 119

Farmyard manure, 165; effect on
soil moisture, 181 ; on fertility,
183 ; comparison with artificials,
166; composition of, 172; losses
in storage, 171 ; time of appli-
cation, 185

Feathers as manure, 200

Feeding stuffs, manurial value of,
188

von Feilitzen's experiments with
phosphatic fertilisers, 153

Fen soils, 40, 123

Fertilisers, annual consumption of,
217

Fertility of the soil, 76, 94; condi-
tions governing, 10, 94

Fibrous material in soil, value of, 37

"Finger and toe," 120, 186, 219

Fish guano, 193

Flocculation, 22

Flue dust as manure, 154, 202

Folding, 37, 113

Food supply and plant growth, 6

Frost, effect in soil, 57

Frosts, spring and autumn, 69

Fruit soils, 69

Gains in nitrogen and nitrate in

soils. 45
Garforth experiments, 152, 162,

163, 226
Gas lime, 226

Grass land, manure for, 213
Grass land map, 68
Grass, suitability for clay land, 111
Greaves, 194
Green manuring, 63, 114
Guano, 191

Gurney's cultivation experiment 82
Gypsum, 144, 176

Hair as manure, 200 '

Hall and Miller, loss of calcium
carbonate from soil, 134

Hall and Voelcker's tables for
manurial values of feeding stuffs,
188

Hansen, experiments at Askor, 167

Hendrick, experiments with phos-
phatic fertilisers, 152; on liquid
manure, 178; experiments with
nitrolim, 138; experiments with
seaweed, 197

Hoeing, 87

Hoofs and horns, 195

Hopkins, Cyril, on loss of lime
from soil, 224

Humus, 36; soluble, 38; physical
properties, 39

Husbandry, schemes of, 104

Hutchinson and MacLennan, effect
of lime and limestone on soil, 221;
determination of carbonates in
soil, 227

Ichaboe guano, 192

Irish Department of Agriculture,

experiments with seaweed, 198;

experiments with phosphatic

fertilisers, 152
Iron compounds in soil, 28
Irrigation, 74

Kainit, 163, 167

Kjeldahl's method for determining
nitrogen, 228, 232

Landlord and tenant, 103

Laterite, 49

Lawes and Gilbert, residual manu-
rial value, 186

Lawes' invention of superphos-
phate, 142

Leather scraps as manure, 201;
waste as manure, 201

Leguminosee and nitrogen fixation,
44

Lime as manure, 221

Limestone as manure, 220, 225

Limiting factors, 3

Liquid manure, 177

Litter, 169

Loams, 116

Index

239

Loess soils, 19, 54
Long manure, 178
Losses from soil, 50

Magnesian limestone, 226
Magnesium salts as manure, 163
Manures and fertilisers, analysis of,

231
Marling, 102
Maryland experiments on lime and

limestone, 225
Meat meal, 194
Mechanical analysis of soil, 13, 108,

230
Milburn, experiments on lime and

limestone, 225
Mixed manures, 209
Morison, composition of basic slag,

150
Mortar rubbish as manure, 226
Mulching, 86
Murray's method of soil analysis,

15

New Jersey experiments on mag-
nesium limestone, 226

Nitrate of lime as fertiliser, 131;
of potash as fertiliser, 131 ; of
soda as fertiliser, 128

Nitrates, amount in soil, 43; esti-
mation of, in soil, 228; in soil,
amount at different seasons, 59

Nitrification, 43

Nitrogen cycle in soil, 47

Nitrogen fixation, 44; in soils,
amount of, 41, 228

Nitrogenous fertilisers, effect on
plants, 129, 139

Nitrolim as fertiliser, 137

Nitrosomonas and nitrobacter, 43

Nobel's method of soil analysis, 13

Oil cakes as manure, 167, 195
Organic matter, effect on soil, 166;
effect of climate in determining
nature of, 49; effect on pro-
ductiveness, 39; methods for
increasing, 112; origin of, 29;
properties of, 36, 50
Organisms living in soil, 46

Palmaer phosphates, 152

Pans, 34, 112

Parkes on drainage, 98

Parkinson's experiments in soil

types, 95
Partial sterilisation, 46
Peat, 40

Peat moss as litter, 169
Peat soils, 123
Pennsylvania, experiments on lime

and limestone, 225
Perchlorates, toxic effect of, 131
Peruvian guano, 192
Phosphates, effect on crops, 143;

estimation of, in soil, 229 ; in

soil, 28
Phosphatic fertilisers, 140
Plant food, 11
Ploughing, effect of, 81
Ploughs, 79
Podsols, 56
Pore-space, 32
Potassic fertilisers, 154
Potassic salts, effect on plants,

161
Potassium compounds in soil, 29;

estimation of, 229
Prairie soils, 40 ; loss of nitrogen

from, 42 ; agriculture on, 70
Protein decomposition in soil, 37

Quartz, 19

Quick acting manures, 166

Kabbit waste as manure, 201
Kainfall map, 66
Rains, winter, bad effect of, 58
Rape cake as manure, 196
Reactive constituents of soil, 21,

134
Red soils, 49

Residual values of manures, 165
Ridging, 89
Rock phosphates, 153
Rolling, 85

Root crop, effect on fertility, 118
Root development and wetness of

soil, 10
Roseworthy Agricultural College

experiments on superphosphates,

146
Rotations, 106, 117
Russian soils, main groups, 56

240

Index

Salt as manure, 164

Sand, properties of, 20

Sandy soils. 111

Saxmundham experiments, 160,

211 •

Schultz, improvement of the Lupitz

estate, 114
Seaweed, 197
Sewage sludge, 203
Shaw on autumn rainfall, 59
Sheep and soil fertility, 113, 118
Shoddy, 199
Short manure, 178
Shutt, loss of nitrogen from soil, 42
Silt, 22

Silty clays, 23, 111
Slow acting manures, 166
Smith on drainage, 98
Snow, supposed fertilising action, 59
Snyder on loss of nitrogen from

soil, 42
Sodium salts as manure, 163
Soil analysis, 227 ; belts and climatic

zones, 52; effect of climate, 48;

formation, 18 ; particles, sizes of,

16 ; sampling, 227 ; type, 95, 105
Somerville, W., experiments on

basic slag, 151
Soot as manure, 202
Sour soils, 51, 96, 219
Spraying weeds, 118
Spring cultivations, 83
Steam ploughing, cases of injury,

34
Steamed bone flour, 141
Storage of dung, changes during,

171
Straw as litter, 170
Subsoil, 34; improvement of, 91
Subsoiling, 90

Sulphocyanides, toxic effect of, 155
Summer cultivations, 86
Superphosphate, 142

Tchernozem (Kussian black earths),
40, 56

Thin soils, 98
Tilth, 77, 96
Trenching, 90
Tundra, 55

Turn-wrest plough, advantage of,
34

Unexhausted values of manure, 186
Unit values, 206

Urine, most valuable part of
manure, 168

Voelcker, J. A., and Hall's tables
for manurial values, 188; green
manuring experiment, 114; acid
soil at Woburn, 135; loss ia
making manure, 170; reports on
manures, 20s

Wagner, Paul, experiments on

basic slag, 149
Waste land, 69
Water supply and plant growth, 6;

content of soil, 32; as affected

by manuring, 181
Wax in soil, 37
Weather: effect of, on soil, 57
Weeds, effect of, 87
Wheat land map, 67
Wheat, record crop, 106
Wheeler on acid soils, 135
W^inter cultivations, 78; dry, good

effect of, 57 ; wet, bad effect of,

58
Woburn experiments. See Voelcker,.

J. A.
Wood ashes as source of potash,

157
Wood, T. B., and Stratton, errors

of held trials, 139 ; loss in making

farmyard manure, 170
Wool scourings as source of potash,

156
Wool waste as manure, 199
Wrightson, John, experiments witlx

basic slag, 149

LIBRARY

FACULTY OF FORESTRY
UNIVERSITY OF TORONTO

S Russell, (Sir) Edward John
633 A student's book on

R8 soils and manures 2d ed.,

1921 rev. and enl.

Forestry

PLEASE DO NOT REMOVE
CARDS OR SLIPS FROM THIS POCKET

UNIVERSITY OF TORONTO LIBRARY

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